Found: 4.91-8~bpo9+1 Happy anniversary! What's up with this one? SMTPUTF8 is still seems not to be enabled. SMTP syntax error in "MAIL FROM: <bob at example.com> SMTPUTF8" H=(DESKTOP001) [10.20.30.271] malformed address: SMTPUTF8 may not follow <bob at example.com>