# smtpd(n) 1.0 smtpd "Tcl SMTP Server Package"

## NAME

smtpd - Tcl SMTP server implementation

## SYNOPSIS

package require Tcl 8.3
package require smtpd ?1.0?

::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 and RFC 2821. 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. In particular, 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 MTA on an Internet connected server, even though we are careful not to evaluate remote user input.

## 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(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 independant 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 ususal 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.
  -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
  -deliver proc
    Callback used to deliver email.
::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 &quot;denied&quot;:

       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.
deliver callback
  The deliver callback is called once a mail message has been successfully passed to the server. 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 $saddr(address) \\
                     [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.

## COPYRIGHT

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.

## KEYWORDS

smtpd, smtp, services, RFC 821, RFC 2821, vwait, socket