SOLVED: SMTP not using AUTH even when configured

Hi,

When I configure an account with IMAP and SMTP, both with SSL/TLS and authentication, I cannot send emails and messages get bounced by the SMTP server "Server error: '554 5.7.1 <recipient@example.com>: Relay access denied". Tested this on Office 365 (2007 build 13029.20236) and Office 2019.

During configuration, Outlook tests the configuration and succeeds. I get the standard "Microsoft Outlook Test Message" in the account's mailbox. In the logs on the SMTP server, I can see the authentication taking place.

Jul 30 17:50:22 smtp postfix/submission/smtpd[22037]: connect from 192.0.2.191.dynamic.example.net[192.0.2.191]

Jul 30 17:50:23 smtp postfix/submission/smtpd[22037]: Anonymous TLS connection established from 191.232.111.77.dynamic.example.net[192.0.2.191]: TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)

Jul 30 17:50:23 smtp postfix/submission/smtpd[22037]: 5EBD2CC75: client=191.232.111.77.dynamic.example.net[192.0.2.191], sasl_method=LOGIN, sasl_username=smtpaccount

Jul 30 17:50:23 smtp postfix/cleanup[23907]: 5EBD2CC75: message-id=<>

Jul 30 17:50:23 smtp postfix/qmgr[82376]: 5EBD2CC75: from=<recipient@example.com>, size=1141, nrcpt=1 (queue active)

Jul 30 17:50:23 smtp postfix/submission/smtpd[22037]: disconnect from 191.232.111.77.dynamic.example.net[192.0.2.191] ehlo=2 starttls=1 auth=1 mail=1 rcpt=1 data=1 commands=7

Jul 30 17:50:24 smtp postfix/lmtp[24544]: 5EBD2CC75: to=<recipient@example.com>, relay=smtp.example.com[/var/run/dovecot/lmtp], delay=0.72, delays=0.36/0.01/0.04/0.31, dsn=2.0.0, status=sent (250 2.0.0 <recipient@example.com> 9bP8K18II1/9YAAA8Ew+PQ Saved)

Jul 30 17:50:24 smtp postfix/qmgr[82376]: 5EBD2CC75: removed

When sending a regular from the account, I can see in the logs that Outlook is NOT using authentication. No sasl_method is found in the logs.

Jul 30 18:08:43 smtp postfix/submission/smtpd[26518]: connect from 191.232.111.77.dynamic.example.net[192.0.2.191]

Jul 30 18:08:44 smtp postfix/submission/smtpd[26518]: Anonymous TLS connection established from 191.232.111.77.dynamic.example.net[192.0.2.191]: TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)

Jul 30 18:08:44 smtp postfix/submission/smtpd[26518]: NOQUEUE: reject: RCPT from 191.232.111.77.dynamic.example.net[192.0.2.191]: 554 5.7.1 <@gmail.com>: Relay access denied; from=<recipient@example.com> to=<@gmail.com> proto=ESMTP helo=<DESKTOPCE8EISJ>

Jul 30 18:08:47 smtp postfix/submission/smtpd[26518]: disconnect from 191.232.111.77.dynamic.example.net[192.0.2.191] ehlo=2 starttls=1 auth=1 mail=1 rcpt=0/1 quit=1 commands=6/7

Can someone please explain to me how I force Outlook to use SMTP AUTH for this account?

Thanks! Barnerd.