Hello Patrick,
Thanks for the response. > The other side offers PLAIN LOGIN, but your smtp client doesn't like that > because those are mechanisms which send identification data in clear (read: > unencrypted). That's because you have this (default) in place: > > smtp_sasl_security_options = noplaintext, noanonymous > > Either you make sure your smtp client uses TLS, while it attempts to > authenticate or you lower the security policy and configure your smtp client > to permit PLAIN and/or LOGIN like this: > > smtp_sasl_security_options = noanonymous I have tried this option as well, and it did not address the issue. Perhaps I should have included full log (see bellow), but the SMTP server won't even advertise AUTH until client starts using TLS as remote server has following in it's master.cf: submission inet n - n - - smtpd -o syslog_name=postfix/submission -o smtpd_tls_security_level=encrypt -o smtpd_sasl_auth_enable=yes -o smtpd_tls_auth_only=yes Here is more detailed log after I set "smtp_sasl_security_options = noanonymous" smtp_1 | 2019-02-16T16:08:21.494186+00:00 xxx postfix/qmgr[86]: 366D7C0D16: from=<r...@docker.smtp.blah.domain.com>, size=188, nrcpt=1 (queue active) smtp_1 | 2019-02-16T16:08:21.558785+00:00 xxx postfix/smtp[88]: smtp_stream_setup: maxtime=300 enable_deadline=0 smtp_1 | 2019-02-16T16:08:21.699962+00:00 xxx postfix/smtp[88]: < SMTPSERVER.DOMAIN.COM[IPADDR]:587: 220 SMTPSERVER.DOMAIN.COM ESMTP Postfix smtp_1 | 2019-02-16T16:08:21.700011+00:00 xxx postfix/smtp[88]: > SMTPSERVER.DOMAIN.COM[IPADDR]:587: EHLO docker.smtp.blah.domain.com smtp_1 | 2019-02-16T16:08:21.736223+00:00 xxx postfix/smtp[88]: < SMTPSERVER.DOMAIN.COM[IPADDR]:587: 250-SMTPSERVER.DOMAIN.COM smtp_1 | 2019-02-16T16:08:21.736254+00:00 xxx postfix/smtp[88]: < SMTPSERVER.DOMAIN.COM[IPADDR]:587: 250-PIPELINING smtp_1 | 2019-02-16T16:08:21.736258+00:00 xxx postfix/smtp[88]: < SMTPSERVER.DOMAIN.COM[IPADDR]:587: 250-SIZE 104857600 smtp_1 | 2019-02-16T16:08:21.736262+00:00 xxx postfix/smtp[88]: < SMTPSERVER.DOMAIN.COM[IPADDR]:587: 250-VRFY smtp_1 | 2019-02-16T16:08:21.736265+00:00 xxx postfix/smtp[88]: < SMTPSERVER.DOMAIN.COM[IPADDR]:587: 250-ETRN smtp_1 | 2019-02-16T16:08:21.736269+00:00 xxx postfix/smtp[88]: < SMTPSERVER.DOMAIN.COM[IPADDR]:587: 250-STARTTLS smtp_1 | 2019-02-16T16:08:21.736276+00:00 xxx postfix/smtp[88]: < SMTPSERVER.DOMAIN.COM[IPADDR]:587: 250-ENHANCEDSTATUSCODES smtp_1 | 2019-02-16T16:08:21.736281+00:00 xxx postfix/smtp[88]: < SMTPSERVER.DOMAIN.COM[IPADDR]:587: 250-8BITMIME smtp_1 | 2019-02-16T16:08:21.736306+00:00 xxx postfix/smtp[88]: < SMTPSERVER.DOMAIN.COM[IPADDR]:587: 250-DSN smtp_1 | 2019-02-16T16:08:21.736310+00:00 xxx postfix/smtp[88]: < SMTPSERVER.DOMAIN.COM[IPADDR]:587: 250 SMTPUTF8 smtp_1 | 2019-02-16T16:08:21.736331+00:00 xxx postfix/smtp[88]: server features: 0x20901f size 104857600 smtp_1 | 2019-02-16T16:08:21.736336+00:00 xxx postfix/smtp[88]: Using ESMTP PIPELINING, TCP send buffer size is 87040, PIPELINING buffer size is 4096 smtp_1 | 2019-02-16T16:08:21.736434+00:00 xxx postfix/smtp[88]: smtp_stream_setup: maxtime=300 enable_deadline=0 smtp_1 | 2019-02-16T16:08:21.736448+00:00 xxx postfix/smtp[88]: > SMTPSERVER.DOMAIN.COM[IPADDR]:587: STARTTLS smtp_1 | 2019-02-16T16:08:21.780254+00:00 xxx postfix/smtp[88]: < SMTPSERVER.DOMAIN.COM[IPADDR]:587: 220 2.0.0 Ready to start TLS ... smtp_1 | 2019-02-16T16:08:21.862152+00:00 xxx postfix/smtp[88]: Trusted TLS connection established to SMTPSERVER.DOMAIN.COM[IPADDR]:587: TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (2048 bits) server-digest SHA256 smtp_1 | 2019-02-16T16:08:21.862200+00:00 xxx postfix/smtp[88]: smtp_stream_setup: maxtime=300 enable_deadline=0 smtp_1 | 2019-02-16T16:08:21.862207+00:00 xxx postfix/smtp[88]: > SMTPSERVER.DOMAIN.COM[IPADDR]:587: EHLO docker.smtp.blah.domain.com .. smtp_1 | 2019-02-16T16:08:21.931001+00:00 xxx postfix/smtp[88]: < SMTPSERVER.DOMAIN.COM[IPADDR]:587: 250-SMTPSERVER.DOMAIN.COM smtp_1 | 2019-02-16T16:08:21.931035+00:00 xxx postfix/smtp[88]: < SMTPSERVER.DOMAIN.COM[IPADDR]:587: 250-PIPELINING smtp_1 | 2019-02-16T16:08:21.931039+00:00 xxx postfix/smtp[88]: < SMTPSERVER.DOMAIN.COM[IPADDR]:587: 250-SIZE 104857600 smtp_1 | 2019-02-16T16:08:21.931043+00:00 xxx postfix/smtp[88]: < SMTPSERVER.DOMAIN.COM[IPADDR]:587: 250-VRFY smtp_1 | 2019-02-16T16:08:21.931047+00:00 xxx postfix/smtp[88]: < SMTPSERVER.DOMAIN.COM[IPADDR]:587: 250-ETRN smtp_1 | 2019-02-16T16:08:21.931052+00:00 xxx postfix/smtp[88]: < SMTPSERVER.DOMAIN.COM[IPADDR]:587: 250-AUTH PLAIN LOGIN smtp_1 | 2019-02-16T16:08:21.931056+00:00 xxx postfix/smtp[88]: < SMTPSERVER.DOMAIN.COM[IPADDR]:587: 250-AUTH=PLAIN LOGIN smtp_1 | 2019-02-16T16:08:21.931064+00:00 xxx postfix/smtp[88]: < SMTPSERVER.DOMAIN.COM[IPADDR]:587: 250-ENHANCEDSTATUSCODES smtp_1 | 2019-02-16T16:08:21.931068+00:00 xxx postfix/smtp[88]: < SMTPSERVER.DOMAIN.COM[IPADDR]:587: 250-8BITMIME smtp_1 | 2019-02-16T16:08:21.931071+00:00 xxx postfix/smtp[88]: < SMTPSERVER.DOMAIN.COM[IPADDR]:587: 250-DSN smtp_1 | 2019-02-16T16:08:21.931075+00:00 xxx postfix/smtp[88]: < SMTPSERVER.DOMAIN.COM[IPADDR]:587: 250 SMTPUTF8 smtp_1 | 2019-02-16T16:08:21.931086+00:00 xxx postfix/smtp[88]: match_string: smtp_sasl_mechanism_filter: plain ~? auth smtp_1 | 2019-02-16T16:08:21.931183+00:00 xxx postfix/smtp[88]: match_string: smtp_sasl_mechanism_filter: plain ~? login smtp_1 | 2019-02-16T16:08:21.931194+00:00 xxx postfix/smtp[88]: match_list_match: PLAIN: no match smtp_1 | 2019-02-16T16:08:21.931222+00:00 xxx postfix/smtp[88]: match_string: smtp_sasl_mechanism_filter: login ~? auth smtp_1 | 2019-02-16T16:08:21.931229+00:00 xxx postfix/smtp[88]: match_string: smtp_sasl_mechanism_filter: login ~? login smtp_1 | 2019-02-16T16:08:21.931234+00:00 xxx postfix/smtp[88]: match_string: smtp_sasl_mechanism_filter: plain ~? auth smtp_1 | 2019-02-16T16:08:21.931237+00:00 xxx postfix/smtp[88]: match_string: smtp_sasl_mechanism_filter: plain ~? login smtp_1 | 2019-02-16T16:08:21.931240+00:00 xxx postfix/smtp[88]: match_list_match: PLAIN: no match smtp_1 | 2019-02-16T16:08:21.931244+00:00 xxx postfix/smtp[88]: match_string: smtp_sasl_mechanism_filter: login ~? auth smtp_1 | 2019-02-16T16:08:21.931247+00:00 xxx postfix/smtp[88]: match_string: smtp_sasl_mechanism_filter: login ~? login smtp_1 | 2019-02-16T16:08:21.931253+00:00 xxx postfix/smtp[88]: server features: 0x20902f size 104857600 smtp_1 | 2019-02-16T16:08:21.931259+00:00 xxx postfix/smtp[88]: Using ESMTP PIPELINING, TCP send buffer size is 87040, PIPELINING buffer size is 4096 smtp_1 | 2019-02-16T16:08:21.931294+00:00 xxx postfix/smtp[88]: maps_find: smtp_sasl_password_maps: SMTPSERVER.DOMAIN.COM: not found smtp_1 | 2019-02-16T16:08:21.931423+00:00 xxx postfix/smtp[88]: maps_find: smtp_sasl_password_maps: hash:/etc/postfix/sasl_passwd(0,lock|fold_fix|utf8_request): [SMTPSERVER.DOMAIN.COM]:587 = username:password smtp_1 | 2019-02-16T16:08:21.931428+00:00 xxx postfix/smtp[88]: smtp_sasl_passwd_lookup: host `SMTPSERVER.DOMAIN.COM' user `username' pass `password' smtp_1 | 2019-02-16T16:08:21.931431+00:00 xxx postfix/smtp[88]: starting new SASL client smtp_1 | 2019-02-16T16:08:21.931444+00:00 xxx postfix/smtp[88]: name_mask: noanonymous smtp_1 | 2019-02-16T16:08:21.931515+00:00 xxx postfix/smtp[88]: smtp_sasl_authenticate: SMTPSERVER.DOMAIN.COM[IPADDR]:587: SASL mechanisms LOGIN smtp_1 | 2019-02-16T16:08:21.931531+00:00 xxx postfix/smtp[88]: warning: SASL authentication failure: No worthy mechs found smtp_1 | 2019-02-16T16:08:21.931802+00:00 xxx postfix/smtp[88]: connect to subsystem private/defer
