dovecot: lmtp(): Fatal: Error reading configuration: Invalid settings: postmaster_address setting not given

I was reconfiguring Postfix to include SpamAssassin, ClamAV and Sieve and somehow I managed to break something 🙂
Emails began to stuck up in queue and /var/log/mail.err was showing:

dovecot: lmtp(5680): Fatal: Error reading configuration: Invalid settings: postmaster_address setting not given

After some research on DuckDuckGo I found the fix:

 nano /etc/dovecot/conf.d/20-lmtp.conf

and add

 protocol lmtp {
 postmaster_address = postmaster@domainname # required
 mail_plugins = quota sieve
 }

then restart postfix and dovecat and we are back in action again.

Some reference here