LDAP groups in Postfix

For a long time I’ve been managing virtual e-mail addresses (the ones you create when you sign up to a web service, so that you know where your spam is originating) using Postfix’s LDAP alias capability.  At the time I was still putting every bit of configuration I could into LDAP–particularly if it was user-id related–and I’ve never had a need to change what was working really well.

N’s school recently decided to distribute the weekly school newsletter via e-mail, and had allowance for one e-mail address per family.  Not wanting the additional overhead of having to have either S or me receive it and then having to forward it to the other, I thought it would be neat to have a single common address that, when items arrived, distributed the mail to multiple boxes.  Of course I took the stupid path of providing the school with a yet-to-be-created e-mail address, foolishly trusting my ability to set the system up before they tried to send anything to it…  but in the end it was not so foolish after all, as unbeknown to me I already had everything I needed to achieve my objective.

Unfortunately the first thing I did was assume that I needed mailing list software.  I installed Mailman, and started to read-up on the process to get it working.  I did this on my yet-to-be-commissioned KVM-hosted mail server (a blog post for another day), and started trying to diagnose why mail wasn’t getting delivered.  I had set up Postfix on this mail server to point to my existing LDAP to test, and thought that there was a problem there (but also started to work out if there was a way to use the LDAP server to manage the Mailman aliases).  I re-found the Postfix LDAP HOWTO, and stumbled over the section entitled “Example: expanding LDAP groups”.  Et voila: multidrop incoming mail without the need for a mailing list manager!

I had always assumed that e-mail aliases were a one-to-one mapping of alias address to real destination.  Not the case: an alias can have multiple destinations.  It doesn’t just apply to LDAP alias support, either: as per the “aliases” man page you can do

name: value1, value2, ...

In my LDAP situation, all I need to do is list the alias in the “mailLocalAddress” attribute of which ever users need to receive mail for that alias.  Done!

I may have to keep Mailman, however.  Shortly after this success, I wondered how cool it would be to have the notification SMS messages for voicemail received at home, that currently go only to S, come to me as well.  I’m using a hosted email-to-SMS gateway service for this, so the “alias” would have to expand to multiple external e-mail addresses.  I’m not sure if you can alias mail addresses that are not in your domain…  I’ll have to try and see–might be easier to do that than subscribing to a Mailman list via SMS-to-email!  🙂