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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 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.

COMMANDS
       ::smtpd::start ?myaddr? ?port?
              Start  the  service  listening on port or the default port 25. If myaddr is given as a domain-style domainstyle
              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 independent channel. Only explicitly tracking and closing these
              sessions, or exiting the server process will close down all the running sessions. This is sim-ilar similar
              ilar to the usual unix daemon practice where the server performs a fork(2) and the client ses-sion session
              sion 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 proce-dure procedure
              dure 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 val-ues. values.
              ues. 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  spe-cific specific
              cific 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  proce-dure procedure
              dure  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(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  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  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)