Provided by: postfix_3.4.5-1ubuntu1_amd64 bug

NAME

       smtpd - Postfix SMTP server

SYNOPSIS

       smtpd [generic Postfix daemon options]

       sendmail -bs

DESCRIPTION

       The  SMTP  server  accepts  network  connection  requests  and  performs zero or more SMTP
       transactions per connection.  Each  received  message  is  piped  through  the  cleanup(8)
       daemon,  and is placed into the incoming queue as one single queue file.  For this mode of
       operation, the program expects to be run from the master(8) process manager.

       Alternatively, the SMTP server be can run  in  stand-alone  mode;  this  is  traditionally
       obtained  with "sendmail -bs".  When the SMTP server runs stand-alone with non $mail_owner
       privileges, it receives mail even while the mail system is not running, deposits  messages
       directly  into  the  maildrop queue, and disables the SMTP server's access policies. As of
       Postfix version 2.3, the SMTP server refuses to receive mail from the network when it runs
       with non $mail_owner privileges.

       The  SMTP  server  implements  a  variety  of  policies  for  connection requests, and for
       parameters given to HELO, ETRN, MAIL FROM, VRFY and RCPT TO commands.  They  are  detailed
       below and in the main.cf configuration file.

SECURITY

       The  SMTP  server  is  moderately  security-sensitive. It talks to SMTP clients and to DNS
       servers on the network. The SMTP server can be run chrooted at fixed low privilege.

STANDARDS

       RFC 821 (SMTP protocol)
       RFC 1123 (Host requirements)
       RFC 1652 (8bit-MIME transport)
       RFC 1869 (SMTP service extensions)
       RFC 1870 (Message size declaration)
       RFC 1985 (ETRN command)
       RFC 2034 (SMTP enhanced status codes)
       RFC 2554 (AUTH command)
       RFC 2821 (SMTP protocol)
       RFC 2920 (SMTP pipelining)
       RFC 3030 (CHUNKING without BINARYMIME)
       RFC 3207 (STARTTLS command)
       RFC 3461 (SMTP DSN extension)
       RFC 3463 (Enhanced status codes)
       RFC 3848 (ESMTP transmission types)
       RFC 4409 (Message submission)
       RFC 4954 (AUTH command)
       RFC 5321 (SMTP protocol)
       RFC 6531 (Internationalized SMTP)
       RFC 6533 (Internationalized Delivery Status Notifications)
       RFC 7505 ("Null MX" No Service Resource Record)

DIAGNOSTICS

       Problems and transactions are logged to syslogd(8) or postlogd(8).

       Depending on the setting of the notify_classes parameter, the postmaster  is  notified  of
       bounces, protocol problems, policy violations, and of other trouble.

CONFIGURATION PARAMETERS

       Changes  to  main.cf  are  picked  up  automatically, as smtpd(8) processes run for only a
       limited amount of time. Use the command "postfix reload" to speed up a change.

       The text below provides only  a  parameter  summary.  See  postconf(5)  for  more  details
       including examples.

COMPATIBILITY CONTROLS

       The following parameters work around implementation errors in other software, and/or allow
       you to override standards in order to prevent undesirable use.

       broken_sasl_auth_clients (no)
              Enable interoperability with remote SMTP clients that implement an obsolete version
              of the AUTH command (RFC 4954).

       disable_vrfy_command (no)
              Disable the SMTP VRFY command.

       smtpd_noop_commands (empty)
              List  of  commands  that  the Postfix SMTP server replies to with "250 Ok", without
              doing any syntax checks and without changing state.

       strict_rfc821_envelopes (no)
              Require that addresses received in SMTP MAIL FROM and RCPT TO commands are enclosed
              with <>, and that those addresses do not contain RFC 822 style comments or phrases.

       Available in Postfix version 2.1 and later:

       smtpd_reject_unlisted_sender (no)
              Request  that  the  Postfix SMTP server rejects mail from unknown sender addresses,
              even when no explicit reject_unlisted_sender access restriction is specified.

       smtpd_sasl_exceptions_networks (empty)
              What remote SMTP clients the Postfix SMTP server will not offer AUTH support to.

       Available in Postfix version 2.2 and later:

       smtpd_discard_ehlo_keyword_address_maps (empty)
              Lookup tables, indexed by the remote SMTP client  address,  with  case  insensitive
              lists  of  EHLO  keywords  (pipelining, starttls, auth, etc.) that the Postfix SMTP
              server will not send in the EHLO response to a remote SMTP client.

       smtpd_discard_ehlo_keywords (empty)
              A case insensitive list of EHLO keywords (pipelining, starttls,  auth,  etc.)  that
              the Postfix SMTP server will not send in the EHLO response to a remote SMTP client.

       smtpd_delay_open_until_valid_rcpt (yes)
              Postpone  the  start  of  an SMTP mail transaction until a valid RCPT TO command is
              received.

       Available in Postfix version 2.3 and later:

       smtpd_tls_always_issue_session_ids (yes)
              Force the Postfix SMTP server to issue a TLS session  id,  even  when  TLS  session
              caching is turned off (smtpd_tls_session_cache_database is empty).

       Available in Postfix version 2.6 and later:

       tcp_windowsize (0)
              An optional workaround for routers that break TCP window scaling.

       Available in Postfix version 2.7 and later:

       smtpd_command_filter (empty)
              A mechanism to transform commands from remote SMTP clients.

       Available in Postfix version 2.9 and later:

       smtpd_per_record_deadline (normal: no, overload: yes)
              Change  the  behavior  of the smtpd_timeout and smtpd_starttls_timeout time limits,
              from a time limit per read or write system call, to a time limit to send or receive
              a  complete  record (an SMTP command line, SMTP response line, SMTP message content
              line, or TLS protocol message).

       Available in Postfix version 3.0 and later:

       smtpd_dns_reply_filter (empty)
              Optional filter for Postfix SMTP server DNS lookup results.

ADDRESS REWRITING CONTROLS

       See the ADDRESS_REWRITING_README document for a detailed  discussion  of  Postfix  address
       rewriting.

       receive_override_options (empty)
              Enable  or  disable  recipient  validation,  built-in content filtering, or address
              mapping.

       Available in Postfix version 2.2 and later:

       local_header_rewrite_clients (permit_inet_interfaces)
              Rewrite message header addresses in mail from these clients and  update  incomplete
              addresses  with  the  domain  name  in $myorigin or $mydomain; either don't rewrite
              message headers from other clients at all, or rewrite message  headers  and  update
              incomplete  addresses with the domain specified in the remote_header_rewrite_domain
              parameter.

BEFORE-SMTPD PROXY AGENT

       Available in Postfix version 2.10 and later:

       smtpd_upstream_proxy_protocol (empty)
              The name of the proxy protocol used by an optional before-smtpd proxy agent.

       smtpd_upstream_proxy_timeout (5s)
              The    time    limit    for    the    proxy    protocol    specified    with    the
              smtpd_upstream_proxy_protocol parameter.

AFTER QUEUE EXTERNAL CONTENT INSPECTION CONTROLS

       As  of  version  1.0,  Postfix  can  be configured to send new mail to an external content
       filter AFTER the mail is queued. This content filter is expected to inject mail back  into
       a (Postfix or other) MTA for further delivery. See the FILTER_README document for details.

       content_filter (empty)
              After   the   message   is  queued,  send  the  entire  message  to  the  specified
              transport:destination.

BEFORE QUEUE EXTERNAL CONTENT INSPECTION CONTROLS

       As of version 2.1, the Postfix SMTP server can be configured to send incoming  mail  to  a
       real-time  SMTP-based  content  filter  BEFORE  mail  is  queued.   This content filter is
       expected to inject mail back  into  Postfix.   See  the  SMTPD_PROXY_README  document  for
       details on how to configure and operate this feature.

       smtpd_proxy_filter (empty)
              The hostname and TCP port of the mail filtering proxy server.

       smtpd_proxy_ehlo ($myhostname)
              How the Postfix SMTP server announces itself to the proxy filter.

       smtpd_proxy_options (empty)
              List  of  options  that  control  how  the  Postfix SMTP server communicates with a
              before-queue content filter.

       smtpd_proxy_timeout (100s)
              The time limit for connecting to a  proxy  filter  and  for  sending  or  receiving
              information.

BEFORE QUEUE MILTER CONTROLS

       As  of version 2.3, Postfix supports the Sendmail version 8 Milter (mail filter) protocol.
       These content filters run outside Postfix. They can inspect the SMTP  command  stream  and
       the  message content, and can request modifications before mail is queued. For details see
       the MILTER_README document.

       smtpd_milters (empty)
              A list of Milter (mail filter) applications for  new  mail  that  arrives  via  the
              Postfix smtpd(8) server.

       milter_protocol (6)
              The mail filter protocol version and optional protocol extensions for communication
              with a Milter application; prior to Postfix 2.6 the default protocol is 2.

       milter_default_action (tempfail)
              The default action when a  Milter  (mail  filter)  application  is  unavailable  or
              mis-configured.

       milter_macro_daemon_name ($myhostname)
              The {daemon_name} macro value for Milter (mail filter) applications.

       milter_macro_v ($mail_name $mail_version)
              The {v} macro value for Milter (mail filter) applications.

       milter_connect_timeout (30s)
              The  time  limit  for  connecting  to  a  Milter (mail filter) application, and for
              negotiating protocol options.

       milter_command_timeout (30s)
              The time limit for sending an SMTP command to a Milter (mail  filter)  application,
              and for receiving the response.

       milter_content_timeout (300s)
              The  time  limit for sending message content to a Milter (mail filter) application,
              and for receiving the response.

       milter_connect_macros (see 'postconf -d' output)
              The macros that are sent to Milter (mail filter) applications after  completion  of
              an SMTP connection.

       milter_helo_macros (see 'postconf -d' output)
              The  macros  that are sent to Milter (mail filter) applications after the SMTP HELO
              or EHLO command.

       milter_mail_macros (see 'postconf -d' output)
              The macros that are sent to Milter (mail filter) applications after the  SMTP  MAIL
              FROM command.

       milter_rcpt_macros (see 'postconf -d' output)
              The  macros  that are sent to Milter (mail filter) applications after the SMTP RCPT
              TO command.

       milter_data_macros (see 'postconf -d' output)
              The macros that are sent to version 4 or higher Milter (mail  filter)  applications
              after the SMTP DATA command.

       milter_unknown_command_macros (see 'postconf -d' output)
              The  macros  that are sent to version 3 or higher Milter (mail filter) applications
              after an unknown SMTP command.

       milter_end_of_header_macros (see 'postconf -d' output)
              The macros that are sent to Milter (mail filter) applications after the end of  the
              message header.

       milter_end_of_data_macros (see 'postconf -d' output)
              The  macros  that  are  sent to Milter (mail filter) applications after the message
              end-of-data.

       Available in Postfix version 3.1 and later:

       milter_macro_defaults (empty)
              Optional list of name=value pairs that specify default values for arbitrary  macros
              that Postfix may send to Milter applications.

       Available in Postfix version 3.2 and later:

       smtpd_milter_maps (empty)
              Lookup tables with Milter settings per remote SMTP client IP address.

GENERAL CONTENT INSPECTION CONTROLS

       The following parameters are applicable for both built-in and external content filters.

       Available in Postfix version 2.1 and later:

       receive_override_options (empty)
              Enable  or  disable  recipient  validation,  built-in content filtering, or address
              mapping.

EXTERNAL CONTENT INSPECTION CONTROLS

       The following parameters are applicable for  both  before-queue  and  after-queue  content
       filtering.

       Available in Postfix version 2.1 and later:

       smtpd_authorized_xforward_hosts (empty)
              What remote SMTP clients are allowed to use the XFORWARD feature.

SASL AUTHENTICATION CONTROLS

       Postfix  SASL  support  (RFC  4954) can be used to authenticate remote SMTP clients to the
       Postfix SMTP server, and to authenticate the Postfix SMTP client to a remote SMTP  server.
       See the SASL_README document for details.

       broken_sasl_auth_clients (no)
              Enable interoperability with remote SMTP clients that implement an obsolete version
              of the AUTH command (RFC 4954).

       smtpd_sasl_auth_enable (no)
              Enable SASL authentication in the Postfix SMTP server.

       smtpd_sasl_local_domain (empty)
              The name of the Postfix SMTP server's local SASL authentication realm.

       smtpd_sasl_security_options (noanonymous)
              Postfix SMTP server SASL security options; as of Postfix 2.3 the list of  available
              features   depends  on  the  SASL  server  implementation  that  is  selected  with
              smtpd_sasl_type.

       smtpd_sender_login_maps (empty)
              Optional lookup table with the SASL login names that own  the  sender  (MAIL  FROM)
              addresses.

       Available in Postfix version 2.1 and later:

       smtpd_sasl_exceptions_networks (empty)
              What remote SMTP clients the Postfix SMTP server will not offer AUTH support to.

       Available in Postfix version 2.1 and 2.2:

       smtpd_sasl_application_name (smtpd)
              The   application   name  that  the  Postfix  SMTP  server  uses  for  SASL  server
              initialization.

       Available in Postfix version 2.3 and later:

       smtpd_sasl_authenticated_header (no)
              Report the SASL authenticated user name in the smtpd(8) Received message header.

       smtpd_sasl_path (smtpd)
              Implementation-specific information that the Postfix SMTP server passes through  to
              the SASL plug-in implementation that is selected with smtpd_sasl_type.

       smtpd_sasl_type (cyrus)
              The SASL plug-in type that the Postfix SMTP server should use for authentication.

       Available in Postfix version 2.5 and later:

       cyrus_sasl_config_path (empty)
              Search  path for Cyrus SASL application configuration files, currently used only to
              locate the $smtpd_sasl_path.conf file.

       Available in Postfix version 2.11 and later:

       smtpd_sasl_service (smtp)
              The service name that  is  passed  to  the  SASL  plug-in  that  is  selected  with
              smtpd_sasl_type and smtpd_sasl_path.

       Available in Postfix version 3.4 and later:

       smtpd_sasl_response_limit (12288)
              The maximum length of a SASL client's response to a server challenge.

STARTTLS SUPPORT CONTROLS

       Detailed information about STARTTLS configuration may be found in the TLS_README document.

       smtpd_tls_security_level (empty)
              The  SMTP TLS security level for the Postfix SMTP server; when a non-empty value is
              specified,   this   overrides   the   obsolete   parameters    smtpd_use_tls    and
              smtpd_enforce_tls.

       smtpd_sasl_tls_security_options ($smtpd_sasl_security_options)
              The  SASL authentication security options that the Postfix SMTP server uses for TLS
              encrypted SMTP sessions.

       smtpd_starttls_timeout (see 'postconf -d' output)
              The time limit for Postfix SMTP server write and read operations during TLS startup
              and shutdown handshake procedures.

       smtpd_tls_CAfile (empty)
              A  file  containing (PEM format) CA certificates of root CAs trusted to sign either
              remote SMTP client certificates or intermediate CA certificates.

       smtpd_tls_CApath (empty)
              A directory containing (PEM format) CA certificates of root  CAs  trusted  to  sign
              either remote SMTP client certificates or intermediate CA certificates.

       smtpd_tls_always_issue_session_ids (yes)
              Force  the  Postfix  SMTP  server  to issue a TLS session id, even when TLS session
              caching is turned off (smtpd_tls_session_cache_database is empty).

       smtpd_tls_ask_ccert (no)
              Ask a remote SMTP client for a client certificate.

       smtpd_tls_auth_only (no)
              When TLS encryption is optional in the Postfix SMTP  server,  do  not  announce  or
              accept SASL authentication over unencrypted connections.

       smtpd_tls_ccert_verifydepth (9)
              The verification depth for remote SMTP client certificates.

       smtpd_tls_cert_file (empty)
              File with the Postfix SMTP server RSA certificate in PEM format.

       smtpd_tls_exclude_ciphers (empty)
              List  of ciphers or cipher types to exclude from the SMTP server cipher list at all
              TLS security levels.

       smtpd_tls_dcert_file (empty)
              File with the Postfix SMTP server DSA certificate in PEM format.

       smtpd_tls_dh1024_param_file (empty)
              File with DH parameters that the Postfix SMTP server should use with non-export EDH
              ciphers.

       smtpd_tls_dh512_param_file (empty)
              File  with  DH parameters that the Postfix SMTP server should use with export-grade
              EDH ciphers.

       smtpd_tls_dkey_file ($smtpd_tls_dcert_file)
              File with the Postfix SMTP server DSA private key in PEM format.

       smtpd_tls_key_file ($smtpd_tls_cert_file)
              File with the Postfix SMTP server RSA private key in PEM format.

       smtpd_tls_loglevel (0)
              Enable additional Postfix SMTP server logging of TLS activity.

       smtpd_tls_mandatory_ciphers (medium)
              The minimum TLS cipher grade that the Postfix SMTP server will use  with  mandatory
              TLS encryption.

       smtpd_tls_mandatory_exclude_ciphers (empty)
              Additional  list of ciphers or cipher types to exclude from the Postfix SMTP server
              cipher list at mandatory TLS security levels.

       smtpd_tls_mandatory_protocols (!SSLv2, !SSLv3)
              The SSL/TLS protocols accepted by  the  Postfix  SMTP  server  with  mandatory  TLS
              encryption.

       smtpd_tls_received_header (no)
              Request  that  the  Postfix  SMTP  server  produces Received:  message headers that
              include information about the protocol and cipher used, as well as the remote  SMTP
              client CommonName and client certificate issuer CommonName.

       smtpd_tls_req_ccert (no)
              With  mandatory TLS encryption, require a trusted remote SMTP client certificate in
              order to allow TLS connections to proceed.

       smtpd_tls_wrappermode (no)
              Run the Postfix SMTP server in the non-standard "wrapper" mode,  instead  of  using
              the STARTTLS command.

       tls_daemon_random_bytes (32)
              The number of pseudo-random bytes that an smtp(8) or smtpd(8) process requests from
              the tlsmgr(8) server in order to seed its internal pseudo random  number  generator
              (PRNG).

       tls_high_cipherlist (see 'postconf -d' output)
              The OpenSSL cipherlist for "high" grade ciphers.

       tls_medium_cipherlist (see 'postconf -d' output)
              The OpenSSL cipherlist for "medium" or higher grade ciphers.

       tls_low_cipherlist (see 'postconf -d' output)
              The OpenSSL cipherlist for "low" or higher grade ciphers.

       tls_export_cipherlist (see 'postconf -d' output)
              The OpenSSL cipherlist for "export" or higher grade ciphers.

       tls_null_cipherlist (eNULL:!aNULL)
              The OpenSSL cipherlist for "NULL" grade ciphers that provide authentication without
              encryption.

       Available in Postfix version 2.5 and later:

       smtpd_tls_fingerprint_digest (md5)
              The  message  digest  algorithm  to  construct   remote   SMTP   client-certificate
              fingerprints   or   public   key   fingerprints   (Postfix   2.9   and  later)  for
              check_ccert_access and permit_tls_clientcerts.

       Available in Postfix version 2.6 and later:

       smtpd_tls_protocols (!SSLv2, !SSLv3)
              List of TLS protocols that the Postfix SMTP server will  exclude  or  include  with
              opportunistic TLS encryption.

       smtpd_tls_ciphers (medium)
              The  minimum  TLS  cipher  grade  that  the  Postfix  SMTP  server  will  use  with
              opportunistic TLS encryption.

       smtpd_tls_eccert_file (empty)
              File with the Postfix SMTP server ECDSA certificate in PEM format.

       smtpd_tls_eckey_file ($smtpd_tls_eccert_file)
              File with the Postfix SMTP server ECDSA private key in PEM format.

       smtpd_tls_eecdh_grade (see 'postconf -d' output)
              The Postfix SMTP server security grade for ephemeral elliptic-curve  Diffie-Hellman
              (EECDH) key exchange.

       tls_eecdh_strong_curve (prime256v1)
              The  elliptic  curve  used by the Postfix SMTP server for sensibly strong ephemeral
              ECDH key exchange.

       tls_eecdh_ultra_curve (secp384r1)
              The elliptic curve used by the Postfix SMTP server for maximally  strong  ephemeral
              ECDH key exchange.

       Available in Postfix version 2.8 and later:

       tls_preempt_cipherlist (no)
              With SSLv3 and later, use the Postfix SMTP server's cipher preference order instead
              of the remote client's cipher preference order.

       tls_disable_workarounds (see 'postconf -d' output)
              List or bit-mask of OpenSSL bug work-arounds to disable.

       Available in Postfix version 2.11 and later:

       tlsmgr_service_name (tlsmgr)
              The name of the tlsmgr(8) service entry in master.cf.

       Available in Postfix version 3.0 and later:

       tls_session_ticket_cipher (Postfix >= 3.0: aes-256-cbc, Postfix < 3.0: aes-128-cbc)
              Algorithm used to encrypt RFC5077 TLS session tickets.

       Available in Postfix version 3.2 and later:

       tls_eecdh_auto_curves (see 'postconf -d' output)
              The prioritized list of elliptic curves supported by the Postfix  SMTP  client  and
              server.

       Available in Postfix version 3.4 and later:

       smtpd_tls_chain_files (empty)
              List  of  one  or  more  PEM  files, each holding one or more private keys directly
              followed by a corresponding certificate chain.

       tls_server_sni_maps (empty)
              Optional lookup tables that map names received from remote SMTP clients via the TLS
              Server  Name  Indication  (SNI)  extension  to the appropriate keys and certificate
              chains.

OBSOLETE STARTTLS CONTROLS

       The following configuration parameters  exist  for  compatibility  with  Postfix  versions
       before 2.3. Support for these will be removed in a future release.

       smtpd_use_tls (no)
              Opportunistic  TLS:  announce  STARTTLS  support to remote SMTP clients, but do not
              require that clients use TLS encryption.

       smtpd_enforce_tls (no)
              Mandatory TLS: announce STARTTLS support to remote SMTP clients, and  require  that
              clients use TLS encryption.

       smtpd_tls_cipherlist (empty)
              Obsolete Postfix < 2.3 control for the Postfix SMTP server TLS cipher list.

SMTPUTF8 CONTROLS

       Preliminary SMTPUTF8 support is introduced with Postfix 3.0.

       smtputf8_enable (yes)
              Enable preliminary SMTPUTF8 support for the protocols described in RFC 6531..6533.

       strict_smtputf8 (no)
              Enable stricter enforcement of the SMTPUTF8 protocol.

       smtputf8_autodetect_classes (sendmail, verify)
              Detect  that  a  message  requires  SMTPUTF8  support for the specified mail origin
              classes.

       Available in Postfix version 3.2 and later:

       enable_idna2003_compatibility (no)
              Enable 'transitional' compatibility between IDNA2003 and IDNA2008, when  converting
              UTF-8 domain names to/from the ASCII form that is used for DNS lookups.

VERP SUPPORT CONTROLS

       With  VERP  style  delivery, each recipient of a message receives a customized copy of the
       message with his/her own recipient address encoded in the envelope  sender  address.   The
       VERP_README  file  describes  configuration  and  operation details of Postfix support for
       variable envelope return path addresses.  VERP style delivery is requested with  the  SMTP
       XVERP  command  or  with the "sendmail -V" command-line option and is available in Postfix
       version 1.1 and later.

       default_verp_delimiters (+=)
              The two default VERP delimiter characters.

       verp_delimiter_filter (-=+)
              The characters  Postfix  accepts  as  VERP  delimiter  characters  on  the  Postfix
              sendmail(1) command line and in SMTP commands.

       Available in Postfix version 1.1 and 2.0:

       authorized_verp_clients ($mynetworks)
              What remote SMTP clients are allowed to specify the XVERP command.

       Available in Postfix version 2.1 and later:

       smtpd_authorized_verp_clients ($authorized_verp_clients)
              What remote SMTP clients are allowed to specify the XVERP command.

TROUBLE SHOOTING CONTROLS

       The  DEBUG_README  document  describes  how to debug parts of the Postfix mail system. The
       methods vary from making the software  log  a  lot  of  detail,  to  running  some  daemon
       processes under control of a call tracer or debugger.

       debug_peer_level (2)
              The  increment  in  verbose  logging level when a remote client or server matches a
              pattern in the debug_peer_list parameter.

       debug_peer_list (empty)
              Optional list of remote client or server hostname or network address patterns  that
              cause   the   verbose  logging  level  to  increase  by  the  amount  specified  in
              $debug_peer_level.

       error_notice_recipient (postmaster)
              The recipient of postmaster notifications about mail  delivery  problems  that  are
              caused by policy, resource, software or protocol errors.

       internal_mail_filter_classes (empty)
              What  categories  of  Postfix-generated  mail  are  subject to before-queue content
              inspection by non_smtpd_milters, header_checks and body_checks.

       notify_classes (resource, software)
              The list of error classes that are reported to the postmaster.

       smtpd_reject_footer (empty)
              Optional information that is appended after each Postfix SMTP  server  4XX  or  5XX
              response.

       soft_bounce (no)
              Safety net to keep mail queued that would otherwise be returned to the sender.

       Available in Postfix version 2.1 and later:

       smtpd_authorized_xclient_hosts (empty)
              What remote SMTP clients are allowed to use the XCLIENT feature.

       Available in Postfix version 2.10 and later:

       smtpd_log_access_permit_actions (empty)
              Enable  logging  of  the  named  "permit"  actions  in SMTP server access lists (by
              default, the SMTP server logs "reject" actions but not "permit" actions).

KNOWN VERSUS UNKNOWN RECIPIENT CONTROLS

       As of Postfix version 2.0, the SMTP server  rejects  mail  for  unknown  recipients.  This
       prevents  the  mail  queue  from  clogging  up  with undeliverable MAILER-DAEMON messages.
       Additional  information   on   this   topic   is   in   the   LOCAL_RECIPIENT_README   and
       ADDRESS_CLASS_README documents.

       show_user_unknown_table_name (yes)
              Display the name of the recipient table in the "User unknown" responses.

       canonical_maps (empty)
              Optional address mapping lookup tables for message headers and envelopes.

       recipient_canonical_maps (empty)
              Optional address mapping lookup tables for envelope and header recipient addresses.

       sender_canonical_maps (empty)
              Optional address mapping lookup tables for envelope and header sender addresses.

       Parameters concerning known/unknown local recipients:

       mydestination ($myhostname, localhost.$mydomain, localhost)
              The  list  of  domains  that  are  delivered via the $local_transport mail delivery
              transport.

       inet_interfaces (all)
              The network interface addresses that this mail system receives mail on.

       proxy_interfaces (empty)
              The network interface addresses that this mail system receives mail on by way of  a
              proxy or network address translation unit.

       inet_protocols (all)
              The  Internet  protocols  Postfix  will  attempt  to  use  when making or accepting
              connections.

       local_recipient_maps (proxy:unix:passwd.byname $alias_maps)
              Lookup tables with all names or addresses of local recipients: a recipient  address
              is   local   when   its   domain   matches   $mydestination,   $inet_interfaces  or
              $proxy_interfaces.

       unknown_local_recipient_reject_code (550)
              The numerical Postfix SMTP server response code when a recipient address is  local,
              and $local_recipient_maps specifies a list of lookup tables that does not match the
              recipient.

       Parameters concerning known/unknown recipients of relay destinations:

       relay_domains (Postfix >= 3.0: empty, Postfix < 3.0: $mydestination)
              What destination domains (and subdomains thereof) this system will relay mail to.

       relay_recipient_maps (empty)
              Optional lookup  tables  with  all  valid  addresses  in  the  domains  that  match
              $relay_domains.

       unknown_relay_recipient_reject_code (550)
              The  numerical  Postfix  SMTP  server  reply  code when a recipient address matches
              $relay_domains, and relay_recipient_maps specifies a list  of  lookup  tables  that
              does not match the recipient address.

       Parameters concerning known/unknown recipients in virtual alias domains:

       virtual_alias_domains ($virtual_alias_maps)
              Postfix  is final destination for the specified list of virtual alias domains, that
              is, domains for which all addresses are aliased to  addresses  in  other  local  or
              remote domains.

       virtual_alias_maps ($virtual_maps)
              Optional lookup tables that alias specific mail addresses or domains to other local
              or remote address.

       unknown_virtual_alias_reject_code (550)
              The  Postfix  SMTP  server  reply   code   when   a   recipient   address   matches
              $virtual_alias_domains,  and  $virtual_alias_maps specifies a list of lookup tables
              that does not match the recipient address.

       Parameters concerning known/unknown recipients in virtual mailbox domains:

       virtual_mailbox_domains ($virtual_mailbox_maps)
              Postfix is final destination for the specified list of domains; mail  is  delivered
              via the $virtual_transport mail delivery transport.

       virtual_mailbox_maps (empty)
              Optional  lookup  tables  with  all  valid  addresses  in  the  domains  that match
              $virtual_mailbox_domains.

       unknown_virtual_mailbox_reject_code (550)
              The  Postfix  SMTP  server  reply   code   when   a   recipient   address   matches
              $virtual_mailbox_domains,  and  $virtual_mailbox_maps  specifies  a  list of lookup
              tables that does not match the recipient address.

RESOURCE AND RATE CONTROLS

       The following parameters limit resource usage by the SMTP  server  and/or  control  client
       request rates.

       line_length_limit (2048)
              Upon  input,  long  lines  are  chopped up into pieces of at most this length; upon
              delivery, long lines are reconstructed.

       queue_minfree (0)
              The minimal amount of free space in bytes in the queue file system that  is  needed
              to receive mail.

       message_size_limit (10240000)
              The maximal size in bytes of a message, including envelope information.

       smtpd_recipient_limit (1000)
              The  maximal  number of recipients that the Postfix SMTP server accepts per message
              delivery request.

       smtpd_timeout (normal: 300s, overload: 10s)
              The time limit for sending a Postfix SMTP  server  response  and  for  receiving  a
              remote SMTP client request.

       smtpd_history_flush_threshold (100)
              The maximal number of lines in the Postfix SMTP server command history before it is
              flushed upon receipt of EHLO, RSET, or end of DATA.

       Available in Postfix version 2.3 and later:

       smtpd_peername_lookup (yes)
              Attempt to look up the remote SMTP  client  hostname,  and  verify  that  the  name
              matches the client IP address.

       The  per  SMTP  client  connection  count  and  request  rate  limits  are  implemented in
       co-operation with the anvil(8) service, and are  available  in  Postfix  version  2.2  and
       later.

       smtpd_client_connection_count_limit (50)
              How many simultaneous connections any client is allowed to make to this service.

       smtpd_client_connection_rate_limit (0)
              The  maximal  number  of  connection attempts any client is allowed to make to this
              service per time unit.

       smtpd_client_message_rate_limit (0)
              The maximal number of message delivery requests that any client is allowed to  make
              to  this  service  per  time  unit,  regardless  of whether or not Postfix actually
              accepts those messages.

       smtpd_client_recipient_rate_limit (0)
              The maximal number of recipient addresses that any client is  allowed  to  send  to
              this  service  per time unit, regardless of whether or not Postfix actually accepts
              those recipients.

       smtpd_client_event_limit_exceptions ($mynetworks)
              Clients that are excluded from smtpd_client_*_count/rate_limit restrictions.

       Available in Postfix version 2.3 and later:

       smtpd_client_new_tls_session_rate_limit (0)
              The maximal number of new (i.e., uncached) TLS sessions that a remote  SMTP  client
              is allowed to negotiate with this service per time unit.

       Available in Postfix version 2.9 and later:

       smtpd_per_record_deadline (normal: no, overload: yes)
              Change  the  behavior  of the smtpd_timeout and smtpd_starttls_timeout time limits,
              from a time limit per read or write system call, to a time limit to send or receive
              a  complete  record (an SMTP command line, SMTP response line, SMTP message content
              line, or TLS protocol message).

       Available in Postfix version 3.1 and later:

       smtpd_client_auth_rate_limit (0)
              The maximal number of AUTH commands that any client is  allowed  to  send  to  this
              service  per time unit, regardless of whether or not Postfix actually accepts those
              commands.

TARPIT CONTROLS

       When a remote SMTP client makes errors, the Postfix SMTP server can insert  delays  before
       responding.  This  can help to slow down run-away software.  The behavior is controlled by
       an error counter that counts the number of errors within an SMTP  session  that  a  client
       makes without delivering mail.

       smtpd_error_sleep_time (1s)
              With  Postfix  version 2.1 and later: the SMTP server response delay after a client
              has   made   more   than   $smtpd_soft_error_limit   errors,   and    fewer    than
              $smtpd_hard_error_limit errors, without delivering mail.

       smtpd_soft_error_limit (10)
              The  number  of  errors  a remote SMTP client is allowed to make without delivering
              mail before the Postfix SMTP server slows down all its responses.

       smtpd_hard_error_limit (normal: 20, overload: 1)
              The maximal number of errors a remote  SMTP  client  is  allowed  to  make  without
              delivering mail.

       smtpd_junk_command_limit (normal: 100, overload: 1)
              The  number  of  junk commands (NOOP, VRFY, ETRN or RSET) that a remote SMTP client
              can send before the Postfix SMTP server starts to increment the error counter  with
              each junk command.

       Available in Postfix version 2.1 and later:

       smtpd_recipient_overshoot_limit (1000)
              The  number of recipients that a remote SMTP client can send in excess of the limit
              specified with $smtpd_recipient_limit, before the Postfix  SMTP  server  increments
              the per-session error count for each excess recipient.

ACCESS POLICY DELEGATION CONTROLS

       As  of  version  2.1,  Postfix can be configured to delegate access policy decisions to an
       external server that runs outside Postfix.  See  the  file  SMTPD_POLICY_README  for  more
       information.

       smtpd_policy_service_max_idle (300s)
              The time after which an idle SMTPD policy service connection is closed.

       smtpd_policy_service_max_ttl (1000s)
              The time after which an active SMTPD policy service connection is closed.

       smtpd_policy_service_timeout (100s)
              The  time  limit for connecting to, writing to, or receiving from a delegated SMTPD
              policy server.

       Available in Postfix version 3.0 and later:

       smtpd_policy_service_default_action (451 4.3.5 Server configuration problem)
              The default action when an SMTPD policy service request fails.

       smtpd_policy_service_request_limit (0)
              The maximal number of requests per SMTPD policy service  connection,  or  zero  (no
              limit).

       smtpd_policy_service_try_limit (2)
              The  maximal  number  of  attempts  to  send an SMTPD policy service request before
              giving up.

       smtpd_policy_service_retry_delay (1s)
              The delay between attempts to resend a failed SMTPD policy service request.

       Available in Postfix version 3.1 and later:

       smtpd_policy_service_policy_context (empty)
              Optional information that the Postfix SMTP server specifies in the "policy_context"
              attribute  of  a  policy  service  request  (originally,  to share the same service
              endpoint among multiple check_policy_service clients).

ACCESS CONTROLS

       The SMTPD_ACCESS_README document gives an introduction  to  all  the  SMTP  server  access
       control features.

       smtpd_delay_reject (yes)
              Wait  until  the  RCPT  TO  command  before  evaluating $smtpd_client_restrictions,
              $smtpd_helo_restrictions and $smtpd_sender_restrictions, or  wait  until  the  ETRN
              command before evaluating $smtpd_client_restrictions and $smtpd_helo_restrictions.

       parent_domain_matches_subdomains (see 'postconf -d' output)
              A  list of Postfix features where the pattern "example.com" also matches subdomains
              of example.com, instead of requiring an explicit ".example.com" pattern.

       smtpd_client_restrictions (empty)
              Optional restrictions that the Postfix SMTP server applies  in  the  context  of  a
              client connection request.

       smtpd_helo_required (no)
              Require  that  a remote SMTP client introduces itself with the HELO or EHLO command
              before sending the MAIL command or other commands that require EHLO negotiation.

       smtpd_helo_restrictions (empty)
              Optional restrictions that the Postfix SMTP server applies  in  the  context  of  a
              client HELO command.

       smtpd_sender_restrictions (empty)
              Optional  restrictions  that  the  Postfix  SMTP server applies in the context of a
              client MAIL FROM command.

       smtpd_recipient_restrictions (see 'postconf -d' output)
              Optional restrictions that the Postfix SMTP server applies  in  the  context  of  a
              client RCPT TO command, after smtpd_relay_restrictions.

       smtpd_etrn_restrictions (empty)
              Optional  restrictions  that  the  Postfix  SMTP server applies in the context of a
              client ETRN command.

       allow_untrusted_routing (no)
              Forward  mail  with  sender-specified   routing   (user[@%!]remote[@%!]site)   from
              untrusted clients to destinations matching $relay_domains.

       smtpd_restriction_classes (empty)
              User-defined aliases for groups of access restrictions.

       smtpd_null_access_lookup_key (<>)
              The  lookup  key  to  be  used  in SMTP access(5) tables instead of the null sender
              address.

       permit_mx_backup_networks (empty)
              Restrict the use of the permit_mx_backup SMTP access feature to only domains  whose
              primary MX hosts match the listed networks.

       Available in Postfix version 2.0 and later:

       smtpd_data_restrictions (empty)
              Optional access restrictions that the Postfix SMTP server applies in the context of
              the SMTP DATA command.

       smtpd_expansion_filter (see 'postconf -d' output)
              What characters are allowed in $name expansions of RBL reply templates.

       Available in Postfix version 2.1 and later:

       smtpd_reject_unlisted_sender (no)
              Request that the Postfix SMTP server rejects mail from  unknown  sender  addresses,
              even when no explicit reject_unlisted_sender access restriction is specified.

       smtpd_reject_unlisted_recipient (yes)
              Request  that the Postfix SMTP server rejects mail for unknown recipient addresses,
              even when no explicit reject_unlisted_recipient access restriction is specified.

       Available in Postfix version 2.2 and later:

       smtpd_end_of_data_restrictions (empty)
              Optional access restrictions that the Postfix SMTP server applies in the context of
              the SMTP END-OF-DATA command.

       Available in Postfix version 2.10 and later:

       smtpd_relay_restrictions           (permit_mynetworks,          permit_sasl_authenticated,
       defer_unauth_destination)
              Access restrictions for mail relay control that the Postfix SMTP server applies  in
              the context of the RCPT TO command, before smtpd_recipient_restrictions.

SENDER AND RECIPIENT ADDRESS VERIFICATION CONTROLS

       Postfix version 2.1 introduces sender and recipient address verification.  This feature is
       implemented by sending probe email messages that are not actually delivered.  This feature
       is  requested  via  the  reject_unverified_sender  and  reject_unverified_recipient access
       restrictions.  The status of verification probes is maintained by  the  verify(8)  server.
       See  the  file  ADDRESS_VERIFICATION_README  for  information  about  how to configure and
       operate the Postfix sender/recipient address verification service.

       address_verify_poll_count (normal: 3, overload: 1)
              How many times to query the verify(8) service for  the  completion  of  an  address
              verification request in progress.

       address_verify_poll_delay (3s)
              The  delay between queries for the completion of an address verification request in
              progress.

       address_verify_sender ($double_bounce_sender)
              The sender address to use in address verification probes; prior to Postfix 2.5  the
              default was "postmaster".

       unverified_sender_reject_code (450)
              The  numerical  Postfix  SMTP  server  response  code  when  a recipient address is
              rejected by the reject_unverified_sender restriction.

       unverified_recipient_reject_code (450)
              The numerical Postfix SMTP server response when a recipient address is rejected  by
              the reject_unverified_recipient restriction.

       Available in Postfix version 2.6 and later:

       unverified_sender_defer_code (450)
              The  numerical  Postfix SMTP server response code when a sender address probe fails
              due to a temporary error condition.

       unverified_recipient_defer_code (450)
              The numerical Postfix SMTP server response when a recipient address probe fails due
              to a temporary error condition.

       unverified_sender_reject_reason (empty)
              The Postfix SMTP server's reply when rejecting mail with reject_unverified_sender.

       unverified_recipient_reject_reason (empty)
              The     Postfix     SMTP     server's    reply    when    rejecting    mail    with
              reject_unverified_recipient.

       unverified_sender_tempfail_action ($reject_tempfail_action)
              The Postfix SMTP server's action  when  reject_unverified_sender  fails  due  to  a
              temporary error condition.

       unverified_recipient_tempfail_action ($reject_tempfail_action)
              The  Postfix  SMTP  server's action when reject_unverified_recipient fails due to a
              temporary error condition.

       Available with Postfix 2.9 and later:

       address_verify_sender_ttl (0s)
              The time between changes in the  time-dependent  portion  of  address  verification
              probe sender addresses.

ACCESS CONTROL RESPONSES

       The following parameters control numerical SMTP reply codes and/or text responses.

       access_map_reject_code (554)
              The  numerical  Postfix  SMTP  server  response  code for an access(5) map "reject"
              action.

       defer_code (450)
              The numerical Postfix SMTP server response code when a remote SMTP  client  request
              is rejected by the "defer" restriction.

       invalid_hostname_reject_code (501)
              The  numerical  Postfix  SMTP  server  response  code  when the client HELO or EHLO
              command parameter is rejected by the reject_invalid_helo_hostname restriction.

       maps_rbl_reject_code (554)
              The numerical Postfix SMTP server response code when a remote SMTP  client  request
              is       blocked      by      the      reject_rbl_client,      reject_rhsbl_client,
              reject_rhsbl_reverse_client,    reject_rhsbl_sender    or    reject_rhsbl_recipient
              restriction.

       non_fqdn_reject_code (504)
              The  numerical  Postfix SMTP server reply code when a client request is rejected by
              the        reject_non_fqdn_helo_hostname,         reject_non_fqdn_sender         or
              reject_non_fqdn_recipient restriction.

       plaintext_reject_code (450)
              The  numerical  Postfix SMTP server response code when a request is rejected by the
              reject_plaintext_session restriction.

       reject_code (554)
              The numerical Postfix SMTP server response code when a remote SMTP  client  request
              is rejected by the "reject" restriction.

       relay_domains_reject_code (554)
              The  numerical  Postfix SMTP server response code when a client request is rejected
              by the reject_unauth_destination recipient restriction.

       unknown_address_reject_code (450)
              The numerical response code when the  Postfix  SMTP  server  rejects  a  sender  or
              recipient address because its domain is unknown.

       unknown_client_reject_code (450)
              The numerical Postfix SMTP server response code when a client without valid address
              <=> name mapping is rejected by the reject_unknown_client_hostname restriction.

       unknown_hostname_reject_code (450)
              The numerical Postfix SMTP server response code when the  hostname  specified  with
              the   HELO   or  EHLO  command  is  rejected  by  the  reject_unknown_helo_hostname
              restriction.

       Available in Postfix version 2.0 and later:

       default_rbl_reply (see 'postconf -d' output)
              The default Postfix SMTP server response template for a request that is rejected by
              an RBL-based restriction.

       multi_recipient_bounce_reject_code (550)
              The  numerical  Postfix SMTP server response code when a remote SMTP client request
              is blocked by the reject_multi_recipient_bounce restriction.

       rbl_reply_maps (empty)
              Optional lookup tables with RBL response templates.

       Available in Postfix version 2.6 and later:

       access_map_defer_code (450)
              The numerical Postfix SMTP server  response  code  for  an  access(5)  map  "defer"
              action, including "defer_if_permit" or "defer_if_reject".

       reject_tempfail_action (defer_if_permit)
              The  Postfix  SMTP  server's  action  when a reject-type restriction fails due to a
              temporary error condition.

       unknown_helo_hostname_tempfail_action ($reject_tempfail_action)
              The Postfix SMTP server's action when reject_unknown_helo_hostname fails due  to  a
              temporary error condition.

       unknown_address_tempfail_action ($reject_tempfail_action)
              The   Postfix   SMTP   server's   action   when   reject_unknown_sender_domain   or
              reject_unknown_recipient_domain fail due to a temporary error condition.

MISCELLANEOUS CONTROLS

       config_directory (see 'postconf -d' output)
              The default location of the Postfix main.cf and master.cf configuration files.

       daemon_timeout (18000s)
              How much time a Postfix daemon process may take to handle a request  before  it  is
              terminated by a built-in watchdog timer.

       command_directory (see 'postconf -d' output)
              The location of all postfix administrative commands.

       double_bounce_sender (double-bounce)
              The  sender  address  of  postmaster  notifications  that are generated by the mail
              system.

       ipc_timeout (3600s)
              The time limit for sending or receiving information over an internal  communication
              channel.

       mail_name (Postfix)
              The  mail  system name that is displayed in Received: headers, in the SMTP greeting
              banner, and in bounced mail.

       mail_owner (postfix)
              The UNIX system account that  owns  the  Postfix  queue  and  most  Postfix  daemon
              processes.

       max_idle (100s)
              The  maximum  amount  of  time  that  an  idle  Postfix daemon process waits for an
              incoming connection before terminating voluntarily.

       max_use (100)
              The maximal number of incoming connections  that  a  Postfix  daemon  process  will
              service before terminating voluntarily.

       myhostname (see 'postconf -d' output)
              The internet hostname of this mail system.

       mynetworks (see 'postconf -d' output)
              The  list  of  "trusted"  remote  SMTP  clients  that  have  more  privileges  than
              "strangers".

       myorigin ($myhostname)
              The domain name that locally-posted mail appears to come  from,  and  that  locally
              posted mail is delivered to.

       process_id (read-only)
              The process ID of a Postfix command or daemon process.

       process_name (read-only)
              The process name of a Postfix command or daemon process.

       queue_directory (see 'postconf -d' output)
              The location of the Postfix top-level queue directory.

       recipient_delimiter (empty)
              The  set  of  characters that can separate a user name from its extension (example:
              user+foo), or a .forward file name from its extension (example: .forward+foo).

       smtpd_banner ($myhostname ESMTP $mail_name)
              The text that follows the 220 status code in the SMTP greeting banner.

       syslog_facility (mail)
              The syslog facility of Postfix logging.

       syslog_name (see 'postconf -d' output)
              A prefix that is prepended to the process name in  syslog  records,  so  that,  for
              example, "smtpd" becomes "prefix/smtpd".

       Available in Postfix version 2.2 and later:

       smtpd_forbidden_commands (CONNECT, GET, POST)
              List  of  commands  that cause the Postfix SMTP server to immediately terminate the
              session with a 221 code.

       Available in Postfix version 2.5 and later:

       smtpd_client_port_logging (no)
              Enable logging of the remote SMTP client port in addition to the  hostname  and  IP
              address.

       Available in Postfix 3.3 and later:

       service_name (read-only)
              The master.cf service name of a Postfix daemon process.

       Available in Postfix 3.4 and later:

       smtpd_reject_footer_maps (empty)
              Lookup  tables,  indexed  by  the complete Postfix SMTP server 4xx or 5xx response,
              with reject footer templates.

SEE ALSO

       anvil(8), connection/rate limiting
       cleanup(8), message canonicalization
       tlsmgr(8), TLS session and PRNG management
       trivial-rewrite(8), address resolver
       verify(8), address verification service
       postconf(5), configuration parameters
       master(5), generic daemon options
       master(8), process manager
       postlogd(8), Postfix logging
       syslogd(8), system logging

README FILES

       Use "postconf readme_directory" or "postconf html_directory" to locate this information.
       ADDRESS_CLASS_README, blocking unknown hosted or relay recipients
       ADDRESS_REWRITING_README, Postfix address manipulation
       BDAT_README, Postfix CHUNKING support
       FILTER_README, external after-queue content filter
       LOCAL_RECIPIENT_README, blocking unknown local recipients
       MILTER_README, before-queue mail filter applications
       SMTPD_ACCESS_README, built-in access policies
       SMTPD_POLICY_README, external policy server
       SMTPD_PROXY_README, external before-queue content filter
       SASL_README, Postfix SASL howto
       TLS_README, Postfix STARTTLS howto
       VERP_README, Postfix XVERP extension
       XCLIENT_README, Postfix XCLIENT extension
       XFORWARD_README, Postfix XFORWARD extension

LICENSE

       The Secure Mailer license must be distributed with this software.

AUTHOR(S)

       Wietse Venema
       IBM T.J. Watson Research
       P.O. Box 704
       Yorktown Heights, NY 10598, USA

       Wietse Venema
       Google, Inc.
       111 8th Avenue
       New York, NY 10011, USA

       SASL support originally by:
       Till Franke
       SuSE Rhein/Main AG
       65760 Eschborn, Germany

       TLS support originally by:
       Lutz Jaenicke
       BTU Cottbus
       Allgemeine Elektrotechnik
       Universitaetsplatz 3-4
       D-03044 Cottbus, Germany

       Revised TLS support by:
       Victor Duchovni
       Morgan Stanley

                                                                                  SMTPD(8postfix)