From what I’ve seen, Dovecot usually fails to start on Debian 13 due to configuration mismatches after the upgrade. The systemd unit itself is generally fine, but small changes in default paths or permissions can block the service. Checking journalctl -u dovecot.service or running dovecot -n is often enough to reveal the exact issue. In one of my cases, a single directive in the config was outdated, and correcting it allowed the service to launch without further issues.
