View source for Procmail/Mail ping

{{DISPLAYTITLE:Create a mail ping with procmail}}

There was a time when as my job included checking if outbound mail was working as part of a morning check routine. After doing it a few times sending mail to an external address and then sending it back again. After a few times doing it I used my gray cells and came up with this procmail recipe cutting. With the time I saved I could now take a longer coffee break :). 

== Prerequisites ==
* procmail
* formail
* MTA (postfix or sendmail to name but 2)

== Howto ==
For this example we assume mail is sent from an address of <tt>*@foobar.office</tt> to <tt>ping@foobar.outside</tt>. In order to prevent the whole world from using your server as ping host the recipe should sport a <tt>From</tt> filter.

=== Recipe === 

 <span class="highlight">PONG_FORMAT=</span>"
 -------------------------------------------------------------------
 pong %s
 -------------------------------------------------------------------
 full pong %s %s %s %s
 -------------------------------------------------------------------
 epoch-nano pong %s
 -------------------------------------------------------------------
 
 -------------------------------------------------------------------
 Original Received Headers:
 -------------------------------------------------------------------
 %s
 -------------------------------------------------------------------
 Notice: This is an automated messages and will only work from the
 foobar.office domain
 -------------------------------------------------------------------
 "
 
 ## ----------------------------------------------------------------------------
 ## morning check
 ## ----------------------------------------------------------------------------
 :0:
 * ^To:.*ping@foobar.outside
 {
 
   <span class="highlight">RECEIVED=</span>`formail -X 'Received'`
   <span class="highlight">PONG_TIME=</span>`date "+%H%M %F %T %z (%Z) %s.%N"`
   :0:
   * ^<span class="highlight">From:</span>.*@foobar.office
   | (<span class="highlight">formail -r</span>; <span class="highlight">printf</span> "$PONG_FORMAT" $PONG_TIME "$RECEIVED";) | \
     <span class="highlight">$SENDMAIL</span> -oi -t -f 'ping@foobar.outside'
 
   # Send to the bit bucket if no match
   :0:
   /dev/null
 }

=== Explanation ===
==== Variables ====
;PONG_FORMAT: Holds the message to in a format usable by the <tt>printf</tt> unix command. When modifiying this message the <tt>printf</tt> arguments must be modified to reflect the number of placeholders.
;RECEIVED: Holds the header of the incoming mail. This is great to find out how many hops the mail took and how long it took at each hop. 
;PONG_TIME: Hold the time when the mail was first processed by the <tt>procmail</tt> rule. The receiving server should be in the same time zone as the sender. If they differ the command can be prefixed with <tt>TZ=<zone> date ...</tt>.
;SENDMAIL: Automatically assigned by <tt>procmail</tt>. Holds the full path to the <tt>sendmail</tt> binary. 

==== Commands ====
;formail -r: Generate an auto-reply header. Will throw away all the existing headers. Hence the <tt>formail -X</tt> command further up in the script!
;printf: Print the new message body based on the <tt>PONG_FORMAT</tt> template.
;sendmail: Send the message straight back to the sender. 
The command <tt>formail -r</tt> and <tt>printf</tt> are executed in a subshell so the message is concatenated before handed to <tt>sendmail</tt>.

=== Sample reply ===
Variable content in green.
 -------------------------------------------------------------------
 pong <span class="input">2149</span> 
 -------------------------------------------------------------------
 full pong <span class="input">2013-12-14 21:49:52 +0100 (CET)</span>
 -------------------------------------------------------------------
 epoch-nano pong <span class="input">1387054192.776386000</span>
 -------------------------------------------------------------------
 
 -------------------------------------------------------------------
 Original Received Headers:
 -------------------------------------------------------------------
 <span class="input">Received: from mxout.foobar.office (mxout.foobar.office [IPv6:XXXX::XXXX])
 	by mail.foobar.outside (Postfix) with ESMTPS id EA6F7C8D901B
 	for <ping@foobar.outside>; Sat, 14 Dec 2013 21:49:49 +0100 (CET)
 Received: from [10.3.4.45] (helo=smtp.foobar.office)
 	by mxout.foobar.office with esmtp (Exim 4.80.1 (FreeBSD))
 	(envelope-from <morning-check@foobar.office>)
 	id 1Vrw9k-000JOr-Q3
 	for ping@foobar.outside; Sat, 14 Dec 2013 21:49:48 +0100
 Received: from [xx.xx.xx.xx] (helo=mail.foobar.office)
 	by smtp.foobar.office with esmtpsa (TLSv1:DHE-RSA-AES256-SHA:256)
 	(Exim 4.80.1 (FreeBSD))
 	(envelope-from <morning-check@foobar.office>)
 	id 1Vrw9k-00080q-N2
 	for ping@foobar.outside; Sat, 14 Dec 2013 21:49:48 +0100</span>
 -------------------------------------------------------------------
 Notice: This is an automated messages and will only work from the
 foobar.office domain
 ------------------------------------------------------------------- 

[[Category: Mail]] [[Category: Procmail]]