I'm using dovecot. I'm having a hell of a time with some versions of Outlook not being able to log into my server over port 993. These clients have to use port 143 and with ssl = required and disable_plaintext_auth = no. I've tried every encryption setting with Outlook (SSL/TLS, STARTTLS, Auto) but none work. I can't get any other combination of settings to work.

What's weird is, other versions of Outlook work fine over port 993 on the same machine. For example, the latest version of outlook that comes with MS 365 works fine.

Any ideas what I can do to get 993 working across all versions of Outlook?

  • 1
    "Some versions of Outlook" is not really specific and makes it difficult to give you good advice... Have you disabled "old and insecure" SSL/TLS protocol versions serverside, such as SSL v3, TLS 1.0 (which might be an issue for older versions) ? – Bob Apr 29 at 15:29
  • I didn't know what the version was. But I have found out since it is 2016. I've got ssl_min_protocol commented out in dovecot. Maybe that's the issue. – StevieD Apr 29 at 15:55
  • Looks like ssl_min_protocol defaults to v1.0. So that's probably not the problem. – StevieD Apr 29 at 15:59

I didn't know what the version was. But I have found out since it is 2016.

If you have the machine at hand, the detailed version information can be viewed via File > Office Account > About OutlooK. Besides, considering that it works in the latest version of outlook for MS 365, I'd suggest checking for and installing all the available updates for Outlook 2016 and see if there would be any improvment.

In case it doesn't work, you may have a look at the dovecot log files to see if any clues can be found.

I also found the thread below which discusess a issue that dovecot cant connect to imaps 993, you could go through the discussion there and check where the informaiton there can be of some help: Dovecot cant connect to imaps 993

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