Provided by: postfix_3.7.4-2build1_amd64 
NAME
tlsproxy - Postfix TLS proxy
SYNOPSIS
tlsproxy [generic Postfix daemon options]
DESCRIPTION
The tlsproxy(8) server implements a two-way TLS proxy. It is used by the postscreen(8)
server to talk SMTP-over-TLS with remote SMTP clients that are not allowlisted (including
clients whose allowlist status has expired), and by the smtp(8) client to support TLS
connection reuse, but it should also work for non-SMTP protocols.
Although one tlsproxy(8) process can serve multiple sessions at the same time, it is a
good idea to allow the number of processes to increase with load, so that the service
remains responsive.
PROTOCOL EXAMPLE
The example below concerns postscreen(8). However, the tlsproxy(8) server is agnostic of
the application protocol, and the example is easily adapted to other applications.
After receiving a valid remote SMTP client STARTTLS command, the postscreen(8) server
sends the remote SMTP client endpoint string, the requested role (server), and the
requested timeout to tlsproxy(8). postscreen(8) then receives a "TLS available"
indication from tlsproxy(8). If the TLS service is available, postscreen(8) sends the
remote SMTP client file descriptor to tlsproxy(8), and sends the plaintext 220 greeting to
the remote SMTP client. This triggers TLS negotiations between the remote SMTP client and
tlsproxy(8). Upon completion of the TLS-level handshake, tlsproxy(8) translates between
plaintext from/to postscreen(8) and ciphertext to/from the remote SMTP client.
SECURITY
The tlsproxy(8) server is moderately security-sensitive. It talks to untrusted clients on
the network. The process can be run chrooted at fixed low privilege.
DIAGNOSTICS
Problems and transactions are logged to syslogd(8) or postlogd(8).
CONFIGURATION PARAMETERS
Changes to main.cf are not picked up automatically, as tlsproxy(8) processes may run for a
long time depending on mail server load. 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.
STARTTLS GLOBAL CONTROLS
The following settings are global and therefore cannot be overruled by information
specified in a tlsproxy(8) client request.
tls_append_default_CA (no)
Append the system-supplied default Certification Authority certificates to the ones
specified with *_tls_CApath or *_tls_CAfile.
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.
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.
tls_disable_workarounds (see 'postconf -d' output)
List or bit-mask of OpenSSL bug work-arounds to disable.
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.
Available in Postfix version 2.9 and later:
tls_legacy_public_key_fingerprints (no)
A temporary migration aid for sites that use certificate public-key fingerprints
with Postfix 2.9.0..2.9.5, which use an incorrect algorithm.
Available in Postfix version 2.11-3.1:
tls_dane_digest_agility (on)
Configure RFC7671 DANE TLSA digest algorithm agility.
tls_dane_trust_anchor_digest_enable (yes)
Enable support for RFC 6698 (DANE TLSA) DNS records that contain digests of
trust-anchors with certificate usage "2".
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.
openssl_path (openssl)
The location of the OpenSSL command line program openssl(1).
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:
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.
Available in Postfix 3.5, 3.4.6, 3.3.5, 3.2.10, 3.1.13 and later:
tls_fast_shutdown_enable (yes)
A workaround for implementations that hang Postfix while shutting down a TLS
session, until Postfix times out.
STARTTLS SERVER CONTROLS
These settings are clones of Postfix SMTP server settings. They allow tlsproxy(8) to load
the same certificate and private key information as the Postfix SMTP server, before
dropping privileges, so that the key files can be kept read-only for root. These settings
can currently not be overruled by information in a tlsproxy(8) client request, but that
limitation may be removed in a future version.
tlsproxy_tls_CAfile ($smtpd_tls_CAfile)
A file containing (PEM format) CA certificates of root CAs trusted to sign either
remote SMTP client certificates or intermediate CA certificates.
tlsproxy_tls_CApath ($smtpd_tls_CApath)
A directory containing (PEM format) CA certificates of root CAs trusted to sign
either remote SMTP client certificates or intermediate CA certificates.
tlsproxy_tls_always_issue_session_ids ($smtpd_tls_always_issue_session_ids)
Force the Postfix tlsproxy(8) server to issue a TLS session id, even when TLS
session caching is turned off.
tlsproxy_tls_ask_ccert ($smtpd_tls_ask_ccert)
Ask a remote SMTP client for a client certificate.
tlsproxy_tls_ccert_verifydepth ($smtpd_tls_ccert_verifydepth)
The verification depth for remote SMTP client certificates.
tlsproxy_tls_cert_file ($smtpd_tls_cert_file)
File with the Postfix tlsproxy(8) server RSA certificate in PEM format.
tlsproxy_tls_ciphers ($smtpd_tls_ciphers)
The minimum TLS cipher grade that the Postfix tlsproxy(8) server will use with
opportunistic TLS encryption.
tlsproxy_tls_dcert_file ($smtpd_tls_dcert_file)
File with the Postfix tlsproxy(8) server DSA certificate in PEM format.
tlsproxy_tls_dh1024_param_file ($smtpd_tls_dh1024_param_file)
File with DH parameters that the Postfix tlsproxy(8) server should use with
non-export EDH ciphers.
tlsproxy_tls_dh512_param_file ($smtpd_tls_dh512_param_file)
File with DH parameters that the Postfix tlsproxy(8) server should use with
export-grade EDH ciphers.
tlsproxy_tls_dkey_file ($smtpd_tls_dkey_file)
File with the Postfix tlsproxy(8) server DSA private key in PEM format.
tlsproxy_tls_eccert_file ($smtpd_tls_eccert_file)
File with the Postfix tlsproxy(8) server ECDSA certificate in PEM format.
tlsproxy_tls_eckey_file ($smtpd_tls_eckey_file)
File with the Postfix tlsproxy(8) server ECDSA private key in PEM format.
tlsproxy_tls_eecdh_grade ($smtpd_tls_eecdh_grade)
The Postfix tlsproxy(8) server security grade for ephemeral elliptic-curve
Diffie-Hellman (EECDH) key exchange.
tlsproxy_tls_exclude_ciphers ($smtpd_tls_exclude_ciphers)
List of ciphers or cipher types to exclude from the tlsproxy(8) server cipher list
at all TLS security levels.
tlsproxy_tls_fingerprint_digest ($smtpd_tls_fingerprint_digest)
The message digest algorithm to construct remote SMTP client-certificate
fingerprints.
tlsproxy_tls_key_file ($smtpd_tls_key_file)
File with the Postfix tlsproxy(8) server RSA private key in PEM format.
tlsproxy_tls_loglevel ($smtpd_tls_loglevel)
Enable additional Postfix tlsproxy(8) server logging of TLS activity.
tlsproxy_tls_mandatory_ciphers ($smtpd_tls_mandatory_ciphers)
The minimum TLS cipher grade that the Postfix tlsproxy(8) server will use with
mandatory TLS encryption.
tlsproxy_tls_mandatory_exclude_ciphers ($smtpd_tls_mandatory_exclude_ciphers)
Additional list of ciphers or cipher types to exclude from the tlsproxy(8) server
cipher list at mandatory TLS security levels.
tlsproxy_tls_mandatory_protocols ($smtpd_tls_mandatory_protocols)
The SSL/TLS protocols accepted by the Postfix tlsproxy(8) server with mandatory TLS
encryption.
tlsproxy_tls_protocols ($smtpd_tls_protocols)
List of TLS protocols that the Postfix tlsproxy(8) server will exclude or include
with opportunistic TLS encryption.
tlsproxy_tls_req_ccert ($smtpd_tls_req_ccert)
With mandatory TLS encryption, require a trusted remote SMTP client certificate in
order to allow TLS connections to proceed.
tlsproxy_tls_security_level ($smtpd_tls_security_level)
The SMTP TLS security level for the Postfix tlsproxy(8) server; when a non-empty
value is specified, this overrides the obsolete parameters smtpd_use_tls and
smtpd_enforce_tls.
tlsproxy_tls_chain_files ($smtpd_tls_chain_files)
Files with the Postfix tlsproxy(8) server keys and certificate chains in PEM
format.
STARTTLS CLIENT CONTROLS
These settings are clones of Postfix SMTP client settings. They allow tlsproxy(8) to load
the same certificate and private key information as the Postfix SMTP client, before
dropping privileges, so that the key files can be kept read-only for root. Some settings
may be overruled by information in a tlsproxy(8) client request.
Available in Postfix version 3.4 and later:
tlsproxy_client_CAfile ($smtp_tls_CAfile)
A file containing CA certificates of root CAs trusted to sign either remote TLS
server certificates or intermediate CA certificates.
tlsproxy_client_CApath ($smtp_tls_CApath)
Directory with PEM format Certification Authority certificates that the Postfix
tlsproxy(8) client uses to verify a remote TLS server certificate.
tlsproxy_client_chain_files ($smtp_tls_chain_files)
Files with the Postfix tlsproxy(8) client keys and certificate chains in PEM
format.
tlsproxy_client_cert_file ($smtp_tls_cert_file)
File with the Postfix tlsproxy(8) client RSA certificate in PEM format.
tlsproxy_client_key_file ($smtp_tls_key_file)
File with the Postfix tlsproxy(8) client RSA private key in PEM format.
tlsproxy_client_dcert_file ($smtp_tls_dcert_file)
File with the Postfix tlsproxy(8) client DSA certificate in PEM format.
tlsproxy_client_dkey_file ($smtp_tls_dkey_file)
File with the Postfix tlsproxy(8) client DSA private key in PEM format.
tlsproxy_client_eccert_file ($smtp_tls_eccert_file)
File with the Postfix tlsproxy(8) client ECDSA certificate in PEM format.
tlsproxy_client_eckey_file ($smtp_tls_eckey_file)
File with the Postfix tlsproxy(8) client ECDSA private key in PEM format.
tlsproxy_client_fingerprint_digest ($smtp_tls_fingerprint_digest)
The message digest algorithm used to construct remote TLS server certificate
fingerprints.
tlsproxy_client_loglevel ($smtp_tls_loglevel)
Enable additional Postfix tlsproxy(8) client logging of TLS activity.
tlsproxy_client_loglevel_parameter (smtp_tls_loglevel)
The name of the parameter that provides the tlsproxy_client_loglevel value.
tlsproxy_client_scert_verifydepth ($smtp_tls_scert_verifydepth)
The verification depth for remote TLS server certificates.
tlsproxy_client_use_tls ($smtp_use_tls)
Opportunistic mode: use TLS when a remote server announces TLS support.
tlsproxy_client_enforce_tls ($smtp_enforce_tls)
Enforcement mode: require that SMTP servers use TLS encryption.
tlsproxy_client_per_site ($smtp_tls_per_site)
Optional lookup tables with the Postfix tlsproxy(8) client TLS usage policy by
next-hop destination and by remote TLS server hostname.
Available in Postfix version 3.4-3.6:
tlsproxy_client_level ($smtp_tls_security_level)
The default TLS security level for the Postfix tlsproxy(8) client.
tlsproxy_client_policy ($smtp_tls_policy_maps)
Optional lookup tables with the Postfix tlsproxy(8) client TLS security policy by
next-hop destination.
Available in Postfix version 3.7 and later:
tlsproxy_client_security_level ($smtp_tls_security_level)
The default TLS security level for the Postfix tlsproxy(8) client.
tlsproxy_client_policy_maps ($smtp_tls_policy_maps)
Optional lookup tables with the Postfix tlsproxy(8) client TLS security policy by
next-hop destination.
OBSOLETE STARTTLS SUPPORT CONTROLS
These parameters are supported for compatibility with smtpd(8) legacy parameters.
tlsproxy_use_tls ($smtpd_use_tls)
Opportunistic TLS: announce STARTTLS support to remote SMTP clients, but do not
require that clients use TLS encryption.
tlsproxy_enforce_tls ($smtpd_enforce_tls)
Mandatory TLS: announce STARTTLS support to remote SMTP clients, and require that
clients use TLS encryption.
tlsproxy_client_use_tls ($smtp_use_tls)
Opportunistic mode: use TLS when a remote server announces TLS support.
tlsproxy_client_enforce_tls ($smtp_enforce_tls)
Enforcement mode: require that SMTP servers use TLS encryption.
RESOURCE CONTROLS
tlsproxy_watchdog_timeout (10s)
How much time a tlsproxy(8) process may take to process local or remote I/O before
it is terminated by a built-in watchdog timer.
MISCELLANEOUS CONTROLS
config_directory (see 'postconf -d' output)
The default location of the Postfix main.cf and master.cf configuration files.
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.
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 3.3 and later:
service_name (read-only)
The master.cf service name of a Postfix daemon process.
SEE ALSO
postscreen(8), Postfix zombie blocker
smtpd(8), Postfix SMTP server
postconf(5), configuration parameters
postlogd(8), Postfix logging
syslogd(8), system logging
LICENSE
The Secure Mailer license must be distributed with this software.
HISTORY
This service was introduced with Postfix version 2.8.
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
TLSPROXY(8postfix)