https://proton.me/cs/support/expiration
Proton Mail message expiration | Proton
Proton Mail allows you to set a time for encrypted messages to expire (automatically delete themselves). Learn how.
proton mailmessage expiration
https://bugzilla.mozilla.org/show_bug.cgi?id=248882
248882 - automatic removal of mail messages from a folder similar to nntp message expiration
RESOLVED (mscott) in Thunderbird - Mail Window Front End. Last updated 2005-09-27.
messages fromautomaticremovalmailfolder