Comment 4 for bug 1393403

Some additional research that touches on this same problem in Ubuntu:

https://www.softprayog.in/troubleshooting/dovecot-imap-error-open-var-mail-username-failed
https://wiki2.dovecot.org/MailLocation/mbox#A.2BAC8-var.2BAC8-mail.2BAC8_dotlocks
https://serverfault.com/questions/814398/dovecot-missing-w-perm-var-mail-were-not-in-group-8mail
https://askubuntu.com/questions/118416/dovecot-cant-compact-mail-folder-var-mail-username

There are a few different ways to set up where Dovecot delivers emails, but /var/mail is one of the more standard locations and perhaps configuring for it should be made more streamlined. I agree with Robie that this work would best be done upstream.

The workarounds are pretty widely documented, so I also agree with him this is not urgent to fix, and should remain in the backlog for now.