Provided by: tcllib_1.19-dfsg-2_all 
NAME
smtpd - Tcl SMTP server implementation
SYNOPSIS
package require Tcl 8.3
package require smtpd ?1.5?
::smtpd::start ?myaddr? ?port?
::smtpd::stop
::smptd::configure ?option value? ?option value ...?
::smtpd::cget ?option?
________________________________________________________________________________________________________________
DESCRIPTION
The smtpd package provides a simple Tcl-only server library for the Simple Mail Transfer Protocol as
described in RFC 821 (http://www.rfc-editor.org/rfc/rfc821.txt) and RFC 2821 (http://www.rfc-
editor.org/rfc/rfc2821.txt). By default the server will bind to the default network address and the
standard SMTP port (25).
This package was designed to permit testing of Mail User Agent code from a developers workstation. It
does not attempt to deliver mail to your mailbox. Instead users of this package are expected to write a
procedure that will be called when mail arrives. Once this procedure returns, the server has nothing
further to do with the mail.
SECURITY
On Unix platforms binding to the SMTP port requires root privileges. I would not recommend running any
script-based server as root unless there is some method for dropping root privileges immediately after
the socket is bound. Under Windows platforms, it is not necessary to have root or administrator
privileges to bind low numbered sockets. However, security on these platforms is weak anyway.
In short, this code should probably not be used as a permanently running Mail Transfer Agent on an
Internet connected server, even though we are careful not to evaluate remote user input. There are many
other well tested and security audited programs that can be used as mail servers for internet connected
hosts.
TLS SECURITY CONSIDERATIONS
This package uses the TLS package to handle the security for https urls and other socket connections.
Policy decisions like the set of protocols to support and what ciphers to use are not the responsibility
of TLS, nor of this package itself however. Such decisions are the responsibility of whichever
application is using the package, and are likely influenced by the set of servers the application will
talk to as well.
For example, in light of the recent POODLE attack
[http://googleonlinesecurity.blogspot.co.uk/2014/10/this-poodle-bites-exploiting-ssl-30.html] discovered
by Google many servers will disable support for the SSLv3 protocol. To handle this change the
applications using TLS must be patched, and not this package, nor TLS itself. Such a patch may be as
simple as generally activating tls1 support, as shown in the example below.
package require tls
tls::init -tls1 1 ;# forcibly activate support for the TLS1 protocol
... your own application code ...
COMMANDS
::smtpd::start ?myaddr? ?port?
Start the service listening on port or the default port 25. If myaddr is given as a domain-style
name or numerical dotted-quad IP address then the server socket will be bound to that network
interface. By default the server is bound to all network interfaces. For example:
set sock [::smtpd::start [info hostname] 0]
will bind to the hosts internet interface on the first available port.
At present the package only supports a single instance of a SMTP server. This could be changed if
required at the cost of making the package a little more complicated to read. If there is a good reason
for running multiple SMTP services then it will only be necessary to fix the options array and the
::smtpd::stopped variable usage.
As the server code uses fileevent(3tcl) handlers to process the input on sockets you will need to run the
event loop. This means either you should be running from within wish(1) or you should vwait(3tcl) on the
::smtpd::stopped variable which is set when the server is stopped.
::smtpd::stop
Halt the server and release the listening socket. If the server has not been started then this
command does nothing. The ::smtpd::stopped variable is set for use with vwait(3tcl).
It should be noted that stopping the server does not disconnect any currently active sessions as
these are operating over an independent channel. Only explicitly tracking and closing these
sessions, or exiting the server process will close down all the running sessions. This is similar
to the usual unix daemon practice where the server performs a fork(2) and the client session
continues on the child process.
::smptd::configure ?option value? ?option value ...?
Set configuration options for the SMTP server. Most values are the name of a callback procedure to
be called at various points in the SMTP protocol. See the CALLBACKS section for details of the
procedures.
-banner text
Text of a custom banner message. The default banner is "tcllib smtpd 1.5". Note that
changing the banner does not affect the bracketing text in the full greeting, printing
status 220, server-address, and timestamp.
-validate_host proc
Callback to authenticate new connections based on the ip-address of the client.
-validate_sender proc
Callback to authenticate new connections based on the senders email address.
-validate_recipient proc
Callback to validate and authorize a recipient email address
-deliverMIME proc
Callback used to deliver mail as a mime token created by the tcllib mime package.
-deliver proc
Callback used to deliver email. This option has no effect if the -deliverMIME option has
been set.
::smtpd::cget ?option?
If no option is specified the command will return a list of all options and their current values.
If an option is specified it will return the value of that option.
CALLBACKS
validate_host callback
This procedure is called with the clients ip address as soon as a connection request has been
accepted and before any protocol commands are processed. If you wish to deny access to a specific
host then an error should be returned by this callback. For example:
proc validate_host {ipnum} {
if {[string match "192.168.1.*" $ipnum]} {
error "go away!"
}
}
If access is denied the client will receive a standard message that includes the text of your error, such
as:
550 Access denied: I hate you.
As per the SMTP protocol, the connection is not closed but we wait for the client to send a QUIT command.
Any other commands cause a 503 Bad Sequence error.
validate_sender callback
The validate_sender callback is called with the senders mail address during processing of a MAIL
command to allow you to accept or reject mail based upon the declared sender. To reject mail you
should throw an error. For example, to reject mail from user "denied":
proc validate_sender {address} {
eval array set addr [mime::parseaddress $address]
if {[string match "denied" $addr(local)]} {
error "mailbox $addr(local) denied"
}
return
}
The content of any error message will not be passed back to the client.
validate_recipient callback
The validate_recipient callback is similar to the validate_sender callback and permits you to
verify a local mailbox and accept mail for a local user address during RCPT command handling. To
reject mail, throw an error as above. The error message is ignored.
deliverMIME callback
] The deliverMIME callback is called once a mail message has been successfully passed to the
server. A mime token is constructed from the sender, recipients and data and the users procedure
it called with this single argument. When the call returns, the mime token is cleaned up so if the
user wishes to preserve the data she must make a copy.
proc deliverMIME {token} {
set sender [lindex [mime::getheader $token From] 0]
set recipients [lindex [mime::getheader $token To] 0]
set mail "From $sender [clock format [clock seconds]]"
append mail "\n" [mime::buildmessage $token]
puts $mail
}
deliver callback
The deliver callback is called once a mail message has been successfully passed to the server and
there is no -deliverMIME option set. The procedure is called with the sender, a list of recipients
and the text of the mail as a list of lines. For example:
proc deliver {sender recipients data} {
set mail "From $sender [clock format [clock seconds]]"
append mail "\n" [join $data "\n"]
puts "$mail"
}
Note that the DATA command will return an error if no sender or recipient has yet been defined.
VARIABLES
::smtpd::stopped
This variable is set to true during the ::smtpd::stop command to permit the use of the vwait(3tcl)
command.
AUTHOR
Written by Pat Thoyts mailto:patthoyts@users.sourceforge.net.
LICENSE
This software is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even
the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the file "license.terms"
for more details.
BUGS, IDEAS, FEEDBACK
This document, and the package it describes, will undoubtedly contain bugs and other problems. Please
report such in the category smtpd of the Tcllib Trackers [http://core.tcl.tk/tcllib/reportlist]. Please
also report any ideas for enhancements you may have for either package and/or documentation.
When proposing code changes, please provide unified diffs, i.e the output of diff -u.
Note further that attachments are strongly preferred over inlined patches. Attachments can be made by
going to the Edit form of the ticket immediately after its creation, and then using the left-most button
in the secondary navigation bar.
KEYWORDS
rfc 2821, rfc 821, services, smtp, smtpd, socket, vwait
CATEGORY
Networking
COPYRIGHT
Copyright (c) Pat Thoyts <patthoyts@users.sourceforge.net>