smtpd(n) Tcl SMTP Server Package smtpd(n) ______________________________________________________________________________
NAME
smtpd - Tcl SMTP server implementation
SYNOPSIS
package require Tcl 8.3
package require smtpd ?1.4?
::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-edi-
tor.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 run-
ning 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.
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 inter-
faces. 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(n) 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(n) 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(n).
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 prac-
tice 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.
-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 vali-
date_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 con-
structed from the sender, recipients and data and the users pro-
cedure 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 suc-
cessfully 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(n) 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 MER-
CHANTABILITY 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 SF Trackers [http://source-
forge.net/tracker/?group_id=12883]. Please also report any ideas for
enhancements you may have for either package and/or documentation.
KEYWORDS
rfc 2821, rfc 821, services, smtp, smtpd, socket, vwait
CATEGORY
Networking
COPYRIGHT
Copyright (c) Pat Thoyts <patthoyts@users.sourceforge.net>
smtpd 1.4 smtpd(n)
Mac OS X 10.8 - Generated Thu Sep 13 05:52:42 CDT 2012