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>