I very successfully operate a I also use it to manage alerts and priorities for a handful of custom systems to special mailboxes. Not every email provider can support such a schema, and until today I was very happy with mine - charging only for a ceiling on daily sends and total mailbox size with unlimited mailboxes. I don't want to go back to managing my own email (though if I have to I will) - do you guys have any recommendations?
Multiple rules can be ANDed or ORed as well, if you don’t want to make a single regex that’s more complex.
They use - and expose - Sieve: https://www.fastmail.com/help/technical/sieve-howto.html
They use qmail and I did something rather similar for myself.