If you run Dovecot (IMAP server) on Debian, upgrading from Bookworm to Trixie is unusually painful. They changed a ton of config options from version 2.3 to 2.4
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I run Mailcow but haven't updated since late last year. Guess I'm gonna continue that trend lol.
I had to spin up a dovecat instance for a phishing pentest the other day and I'm still recovering from the experience