Hi Zang.
was testing with the postmaster account to send email to external email.
Follows part of log when i do that using roundcube:
Jun 28 13:04:25 mail2 postfix/submission/smtpd[79586]: connect from localhost[127.0.0.1]
Jun 28 13:04:25 mail2 postfix/submission/smtpd[79586]: Anonymous TLS connection established from localhost[127.0.0.1]: TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)
Jun 28 13:04:26 mail2 postfix/submission/smtpd[79586]: 4070D25F6B7: client=localhost[127.0.0.1], sasl_method=LOGIN, sasl_username=postmaster@petry.net.br
Jun 28 13:04:26 mail2 postfix/cleanup[79589]: 4070D25F6B7: message-id=<7d49fcef4efc0749aa1c43b284e48b17@petry.net.br>
Jun 28 13:04:26 mail2 postfix/qmgr[94456]: 4070D25F6B7: from=<postmaster@petry.net.br>, size=3214, nrcpt=1 (queue active)
Jun 28 13:04:26 mail2 roundcube: <2uucu4ep> User postmaster@petry.net.br [186.249.196.54]; Message for jorge1@k2s.in; 250: 2.0.0 Ok: queued as 4070D25F6B7
Jun 28 13:04:26 mail2 postfix/submission/smtpd[79586]: disconnect from localhost[127.0.0.1] ehlo=2 starttls=1 auth=1 mail=1 rcpt=1 data=1 quit=1 commands=8
Jun 28 13:04:26 mail2 amavis[83348]: (83348-03) NOTICE: reconnecting in response to: err=2006, HY000, DBD::mysql::st execute failed: MySQL server has gone away at (eval 110) line 173.
Jun 28 13:04:26 mail2 postfix/10025/smtpd[79594]: connect from localhost[127.0.0.1]
Jun 28 13:04:26 mail2 postfix/10025/smtpd[79594]: C32C225F6FC: client=localhost[127.0.0.1]
Jun 28 13:04:26 mail2 postfix/cleanup[79589]: C32C225F6FC: message-id=<7d49fcef4efc0749aa1c43b284e48b17@petry.net.br>
Jun 28 13:04:26 mail2 postfix/10025/smtpd[79594]: disconnect from localhost[127.0.0.1] ehlo=1 mail=1 rcpt=1 data=1 quit=1 commands=5
Jun 28 13:04:26 mail2 postfix/qmgr[94456]: C32C225F6FC: from=<postmaster@petry.net.br>, size=4274, nrcpt=1 (queue active)
Jun 28 13:04:26 mail2 amavis[83348]: (83348-03) Passed CLEAN {RelayedInternal}, ORIGINATING/MYNETS LOCAL [127.0.0.1]:15613 <postmaster@petry.net.br> -> <jorge1@k2s.in>, Queue-ID: 4070D25F6B7, Message-ID: <7d49fcef4efc0749aa1c43b284e48b17@petry.net.br>, mail_id: uZHHyYTokakA, Hits: -, size: 3214, queued_as: C32C225F6FC, dkim_new=dkim:petry.net.br, 422 ms
Jun 28 13:04:26 mail2 amavis[83348]: (83348-03) Passed CLEAN, <postmaster@petry.net.br> -> <jorge1@k2s.in>, Hits: -, tag=0, tag2=0, kill=0, queued_as: C32C225F6FC, L/0/0/0
Jun 28 13:04:26 mail2 postfix/amavis/smtp[79590]: 4070D25F6B7: to=<jorge1@k2s.in>, relay=127.0.0.1[127.0.0.1]:10026, delay=0.61, delays=0.17/0.01/0/0.43, dsn=2.0.0, status=sent (250 2.0.0 from MTA(smtp:[127.0.0.1]:10025): 250 2.0.0 Ok: queued as C32C225F6FC)
Jun 28 13:04:26 mail2 postfix/qmgr[94456]: 4070D25F6B7: removed
Jun 28 13:04:32 mail2 postfix/smtp[79595]: Untrusted TLS connection established to mx.imagik.com.br[170.84.18.10]:25: TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)
Jun 28 13:04:52 mail2 postfix/smtp[79595]: C32C225F6FC: to=<jorge1@k2s.in>, relay=mx.imagik.com.br[170.84.18.10]:25, delay=26, delays=0.01/0.01/5.9/20, dsn=5.1.1, status=bounced (host mx.imagik.com.br[170.84.18.10] said: 550 5.1.1 <jorge1@k2s.in>: Recipient address rejected: User unknown in virtual mailbox table (in reply to RCPT TO command))
Jun 28 13:05:12 mail2 postfix/cleanup[79589]: F1E7025F6B7: message-id=<20180628160512.F1E7025F6B7@mail2.petry.net.br>
Jun 28 13:05:12 mail2 postfix/bounce[79611]: C32C225F6FC: sender non-delivery notification: F1E7025F6B7
Jun 28 13:05:12 mail2 postfix/qmgr[94456]: F1E7025F6B7: from=<>, size=6421, nrcpt=1 (queue active)
Jun 28 13:05:12 mail2 postfix/qmgr[94456]: C32C225F6FC: removed
Jun 28 13:05:13 mail2 postfix/pipe[79621]: F1E7025F6B7: to=<postmaster@petry.net.br>, relay=dovecot, delay=0.02, delays=0/0.01/0/0.01, dsn=5.3.0, status=bounced (command line usage error. Command output: lda: Fatal: Invalid -f parameter: Missing domain )
Jun 28 13:05:13 mail2 postfix/qmgr[94456]: F1E7025F6B7: removed