Subdomain addressing on a custom domain (or even protonmail.com/ch)
I'm a heavy user of subdomain addressing, for the last ~15 years, as described here https://www.fastmail.com/help/receive/addressing.html
This feature is more reliable than the + plus/sub-addressing feature that protonmail already has, and is a unfortunately a blocking feature for me to move my personal mail to be hosted on protonmail.
I'm looking this to be implemented for custom domains, but it could clearly also be provided for protonmail.com/ch or pm.me users.
So in it's simplicity, one could register to a service with e.g. email@example.com instead of firstname.lastname@example.org (or e.g. email@example.com if you want to reserve the immediate subdomains).
This is stopping me from migrating from FastMail to ProtonMail, I've signed up to all of my online accounts with various subdomain addresses so it would be way too much work to migrate them all to sub-addresses.
This is stopping me from migrating from Fastmail too.
I need this feature too