The need arose to have a specific email address round-robin (e.g., cycle through a collection of destination email addresses).

A solution was achieved through use of procmail and a little perl script. It probably could be done more easily and/or better, but I figured other people might find this interesting.

So, first, an alias was created in /etc/aliases (used by postfix in this case, but it should work for sendmail, and variants should work for other MTAs):

rrtest:         |"/usr/bin/procmail -m /etc/postfix/roundrobin_procmail.rc"

Then, the following file was saved as /etc/postfix/roundrobin_procmail.rc:

:0 w:/tmp/rrlock
{
        :0
                dest=|/etc/postfix/rr.pl
        :0
                ! ${dest}
}

And then, of course, we need the perl program. Here’s /etc/postfix/rr.pl:

#!/bin/perl
# ----------------------------------------------------------
@recipients = (
'address1@sample.com',
'address2@sample.com',
'address3@sample.com'
);

$index_file = 'rr-index.txt';

# ----------------------------------------------------------

$index_exists = 1;
open(IN,";
        close(IN);
        $index++;
        }
else
        {
        $index = 0;
        }


if ($index > $#recipients)
        {
        $index = 0;
        }
open(OUT,">/tmp/${index_file}");
print OUT "$index\n";
close(OUT);

print STDOUT $recipients[$index];

exit 0;

Elegant? Not really. But it seems to work 🙂