Desirables
* Aliases: forwarding between addresses <https://en.wikipedia.org/wiki/Email_alias>
* Subaddressing: address suffixes aliasing the same mailbox <https://en.wikipedia.org/wiki/Email_address#Subaddressing>
* Standard protocols IMAPS and SMTPS

Cost-free
* <https://systemli.org>: Needs invitation. Sieve. Onion service.
* <https://dismail.de>
* <https://protonmail.com>: No direct IMAP or SMTP without a paid-for Bridge.
* <https://disroot.org>
* <https://ctemplar.com>: No aliases (paid feature), green energy, no IMAP or SMTP

For a price
* <https://mailbox.org> Accepting bank transfers.
* <https://mailfence.com> Doesn't accept bank trasnfer. Bitcoin & Litecoin.
* <https://www.migadu.com> Doesn't accept bank transfers. Bitcoin.
* <https://posteo.de> Accepting bank transfers. Aliases
* <https://nomagic.uk>

Other lists
For longer and more analytical listings:

* <https://dismail.de/serverlist.html>
* <https://www.safetydetectives.com/blog/email-comparison>
* <https://digdeeper.neocities.org/ghost/email.html>