Hello,
I am running OpenBSD 6.5 with OpenSMTPD and dovecot and if I send an email to an invalid email address, I do not get a bounce back from OpenSMTPD telling me that the email address is invalid. So this means I never know that I made a mistake in sending my email.
I have the same problem (my logs look the same) and are very interested in a solution.
$ cat /etc/mail/smtpd.conf v4adr = 192.168.0.202 v6adr = 1:2:3:4:5:6:7:8 hostn = example.com table aliases file:/etc/mail/aliases table domains file:/etc/mail/domains table ma2user file:/etc/mail/mail2user table legladr file:/etc/mail/legal-mail-from table loclonl file:/etc/mail/local-mail-only table pwdauth file:/etc/mail/pwdauth table passwd file:/etc/mail/passwd pki $hostn cert "/etc/mail/example.com_Cert.pem" pki $hostn key "/etc/mail/example.com_Key.pem" smtp max-message-size 150M listen on lo0 listen on $v4adr port 465 smtps \ hostname $hostn pki $hostn \ mask-src auth <passwd> senders <legladr> listen on $v6adr port 465 smtps \ hostname $hostn pki $hostn \ mask-src auth <passwd> senders <legladr> listen on $v4adr port 587 tls-require \ hostname $hostn pki $hostn \ auth <passwd> senders <legladr> listen on $v6adr port 587 tls-require \ hostname $hostn pki $hostn \ auth <passwd> senders <legladr> action "receivedLocally" lmtp "/var/dovecot/lmtp" alias <aliases> action "receivedRemotely" lmtp "/var/dovecot/lmtp" virtual <ma2user> action "relay2MX" relay \ host smtps://e...@mx.example.com:465 \ auth <pwdauth> \ helo $hostn \ src $v6adr match for local action "receivedLocally" match auth from any for domain <domains> action "receivedRemotely" match auth from any for any mail-from <loclonl> action "receivedRemotely" match auth from any for any action "relay2MX"