RE: https://social.tchncs.de/@Lapizistik/116087161953914165

I can pull mail addresses out of thin air.

My mailer knows about

 local_part_suffix = +* : -*
 local_part_suffix_optional

so you can mail to kris@..., but also to kris+keks@... or kris-keks@...

They will all go to the kris user account,and there will be X-local-part-suffix: keks set for any mail to kris-keks@....

Of course, I don't want all of that in my inbox.

:0
* ^X-local-part-suffix:.*kris-\/[^@]+
$MAILDIR/.special.`echo $MATCH | sed -e 's!([^)]*)!!g' -e 's![^a-zA-Z0-9_-]!_!g' | tr A-Z a-z`/

The what:

Anything that matches X-local-part-suffix: kris-something@... will be caught by that rule.

We take something from the rule, lowercase it, and replace all characters that are not letters or numbers or _ or - with a _. We then push that into the folder INBOX/special/something or whatever that replacement produces.

So mail to kris-keks@... goes to the folder INBOX/special/keks. If it doesn't exist we create it.