Postfix smtp does not work outlook 365

I have a problem with postfix that I can´t send by outlook 365, I can download the emails by pop/imap but not send.

All the other tools I tested worked, google smtp, thunderbird, applemail … But not outlook, this is taking my sleep.

Does anyone know a solution?


I solved it! If anyone else has this problem just need to add auth_mechanisms to /etc/dovecot/dovecot.conf and restart dovecot.

auth_mechanisms = plain login

That way he will be able to log in smtp to outlook on mac.

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Thanks! It is working! This issue occur me a headache a long time ago…

The biggest question: if we are talking about SMTP (postfix), why Dovecot bring the solution?


As described in this answer here I would recommend checking your logs for more information.

Run this command:

tail -f /var/log/mail.err /var/log/mail.log /var/log/dovecot.log /var/log/spamassassin/spamd.log

And then try to authenticate via Outlook and try to send an email. This should populate the logs and the information would give you a good starting point for further troubleshooting.

Let me know how it goes! Regards, Bobby