Procmail

This page lists a few tricks which could be used by Gentoo developers and other procmail users to clean up / sort excessive mail.

Please note that in order for any of the listed tips to work, procmail has to be enabled first. On dev.gentoo.org, this is done through setting the ~/.forward file:

Removing duplicate (CC) mails from mailing lists
The mailing list etiquette requires people to CC all the people involved in a particular thread in replies to the mailing list, in case any of them is not subscribed. For that reason, people being subscribed often receive double replies -- first directly from the person, then from the mailing list.

A solution for that is to discard the directly received mail which is addressed to the mailing list address as well:

In this case, mails which were addressed to the particular mailing list but didn't come from the mailing list directly are moved directly to Trash folder. Alternatively, /dev/null can be used to discard them completely.