How to enable piping in /etc/aliases?

Which mailserver? In postfix, it's enabled by default. Also, if you're not already committed to a particular MTA, postfix has nice automatic support for mailman (or, vice-versa, mailman make support in postfix nice.)

I have Exim4 installed. Do you know how to make it work with Exim4 by enabling piping? I didn't think the piping thingy was tied to Exim4 and that it could be solved by replacing it. I'll see if that can be an option. Thanks for the tip.

Take a look at this. In particular the comment where it says "In fact in Debian Sarge's standard exim configuration pipes in /etc/aliases are not honored anyway."

The main article plus the rest of that comment may solve your problem.

@pclissold:

Take a look at this. In particular the comment where it says "In fact in Debian Sarge's standard exim configuration pipes in /etc/aliases are not honored anyway."

The main article plus the rest of that comment may solve your problem.

Thanks for the tip. I'll look into it and report back.

I went with the "install postfix instead of exim4" option and it worked out of the box. Thanks everyone for your help.