Postfix smtp does not work outlook 365

September 6, 2019 111 views
Email CentOS

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?

1 comment
  • 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.

1 Answer


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!

  • These commands do not work on my system. But I have the postfix logs.
    Error message:
    Message successfully:

    I changed the email names and ips for privacy.

    The ports are open:

    master  11356    root   18u  IPv4 11361836      0t0  TCP *:submission (LISTEN)
    master  11356    root   19u  IPv6 11361837      0t0  TCP *:submission (LISTEN)
    smtpd   15250 postfix    6u  IPv4 11361836      0t0  TCP *:submission (LISTEN)
    smtpd   15250 postfix    7u  IPv6 11361837      0t0  TCP *:submission (LISTEN)

    I also found out that it is a mac/os outlook specific issue, unfortunately microsoft didn’t want to support me.

    • Hello,

      This indeed sounds like a Mac Outlook specific problem as I’m unable to find anything specific in the logs that could be pointing to a configuration problem.

      Have you tried using the Mac Mail instead to see if that works?


      • Yes, all other email programs work. Apple mail, thunderbird, google smtp … until outlook on iphone.

        I solved adding auth_mechanisms to /etc/dovecot/dovecot.conf and restart dovecot.

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