Dovecot 2.4 SSL Certificate Configuration Change
ssl_cert becomes ssl_server_cert_file — and other encryption changes.
Dovecot 2.4 renamed several SSL settings. If your mail server's TLS stopped working after the upgrade, this is probably why.
In Dovecot 2.3, SSL certificates were configured with ssl_cert and ssl_key. In 2.4, these are renamed:
ssl_cert→ssl_server_cert_filessl_key→ssl_server_key_file
The old names are silently ignored — your server starts, but TLS connections fail because no certificate is loaded. This is one of the most common issues after upgrading.
Additionally, the ssl = required setting has changed syntax. Check Willem's complete migration guide for the exact new format.
From the full Dovecot 2.4 migration guide.