I finally got around to upgrading to upgrading from Debian bookworm to trixie. As usual, the Debian parts were fine but I did hit an issue with config changes upgrading from Dovecot 2.3 in bookworm to Dovecot 2.4 in trixie.

The biggest changes are documented elsewhere on the internet and Dovecot also calls out the changes. These are splitting up of mail_location into mail_driver, mail_home, and mail_path. Another is ssl_cert and ssl_key were both renamed and now take the paths to a file rather than needing a < to read the entire file. Easy changes overall.

However, the updated mail_path was not enough to work as I would get login errors in Thunderbird about Dovecot not being able to create the inbox path. The Dovecot journal had this error for me:

Error: Mailbox INBOX: Failed to autocreate mailbox: Permission denied

Turns out Debian has a modification that both warns about using mbox and then assumes you will use it anyway. It sets mail_inbox_path to /var/mail/%{user}. I’m using Maildir though a similar issue would exist for sdbox and mdbox I believe. Dovecot even calls out setting it is unlikely to be what you want.

If your inbox does not reside in some weird location, you should not set this setting to any value.

Because this setting is changed in a file provided by a Debian package, I will need to override it. I changed mail_inbox_path to the right path for my INBOX and then Dovecot was happy and I could once again read my email.