Resources

For further reading and research, I recommend the following websites and mailing lists:

Procmail:

• Procmail FAQ: https://www.iki.fi/~era/procmail/
• The procmail mailing list archive: https://www.rosat.mpe-garching.mpg.de/mailing-lists/procmail/

Spam:

• The Official SPAM-L FAQ: https://www.ot.com/~dmuth/spam-l/
• Fight Spam on the Internet: https://spam.abuse.net/