Turns out this wasn't something wrong with the postfix. But in case someone will run into the same issue -- here is how I addressed this problem:
Alpine 3.9 splitted package libsasl (which used to contain liblogin and libplain[1]) into three: libsasl[2], cyrus-sasl-plain[3] and cyrus-sasl-login [4]. Installing these two extra packages didn't solve my problem. Then I started looking throughout the changelogs of the cyrus-sasl and... something made me look into config dir of the sasl. I accidentally instead of cd used mkdir and after few more steps I ran "postfix flush" and this got email relayed to the upstream server. Turns out, "mkdir /etc/sasl2" fixed the problem. I've verified on fresh container. Thanks everyone who helped. [1]: https://pkgs.alpinelinux.org/contents?file=&path=&name=libsasl&branch=v3.8&repo=main&arch=x86_64 [2]: https://pkgs.alpinelinux.org/contents?file=&path=&name=libsasl&branch=v3.9&repo=main&arch=x86_64 [3]: https://pkgs.alpinelinux.org/contents?file=&path=&name=cyrus-sasl-plain&branch=v3.9&repo=main&arch=x86_64 [4]: https://pkgs.alpinelinux.org/contents?file=&path=&name=cyrus-sasl-login&branch=v3.9&repo=main&arch=x86_64 16.02.2019, 11:22, "sashk" <b...@sashk.xyz>: > 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
