$19/year for minimum. Based in Switzerland
Alternatives:
FreeLists.org
Gaggle.email (not happy that they genericize the word Listserv)
Top contenders:
Mailfence - Belgian, e3.50/mo
Mailbox.org - German, e3/mo; e1/mo plan only allows custom domain for "team accounts" (more than one account? does the first one have to do the e3 plan?)
Posteo - German, no personal domains
Runbox - Norwegian, inexpensive
Soverin: Dutch, € 3.25/mo
Protonmail or Kolab - Swiss, a bit steep; Protonmail e4.00/mo paid annually
Infomaniak: e1.50/mo (..?)
Pobox: US-based, seems like only the expensive account is for custom domains
Msgsafe.io: defunct
Countermail: Swedish, ~$4/mo
Disroot: Dutch, free but requires donation to use custom domain
Spaceship may not be super-private, but it's economical and US-based
Porkbun: Oregon, $24/year but only 20 max addresses
Getting the syntax right is hard! And it's hiding under /usr/local/cyrus/sbin/
https://www.linuxquestions.org/questions/linux-software-2/cyrus-ipurge-not-working-317640-print/
[adding a verified avatar logo using open protocols, for mail received in Gmail]
There's gotta be a way to make Majordomo cooperate, where it doesn't modify the message after being signed.
based around dovecot, but has the basic structure
This might be useful to let some less-certain spam detection to put things into the Spam folder, but hide the more obvious stuff completely.
This is the one I installed in the 90's on my home machine, and used in conjunction with fetchmail to retrieve messages over POP. Always the rebel, I had to try something besides mail and pine, and elm seemed too similar to both.