Both exim and postfix are more than capable of doing what you need, best advice is to pick the one that's easiest for you to use and/or most familiar with.

As for dealing with forwards to gmail and into scripts best way to do this is with a global aliases file (usually kept in /etc/aliases or /etc/mail/aliases). 

Postfix or exim: Automated/Programmatic and forwarded email setup
I would like to have the following output:


Text

(a) Text

Text
Text


That is, after a subitem, I want to return to the last number without creating a new one. Is there any way to do this without ERT?
