Mac 2016 Outlook v15.9 certificate problem

I'm having the same problem.  We're using self-hosted Exchange, not Office 365.  The certificate that appears is the SSL certificate for the company that hosts the web site for my root domain.  It is not a certificate for my Exchange servers.

When I do a Wireshark packet capture, I can see that Outlook is attempting to contact the root domain (example.com).  This happens on every launch, even though I've manually configured the account to connect to my exchange servers (outlook.example.com).  When I click CANCEL on the SSL trust screen, it establishes TLS to the correct server.

Note that we have our autodiscover.example.com domain setup correctly and Windows clients are working properly.  The Wireshark capture does not show an attempt to lookup autodiscover, it only shows a query to the root domain.

In reply to the community moderator advising people to "Always Trust", this is horrible advice.  In my case, I would assume that once the SSL connection is successfully established, Outlook would potentially transmit my credentials.  In my case, since I don't trust the people who host my company's public web server with my credentials, this would be very bad.

This issue is still not fixed.  To anyone at Microsoft, if you are looking at this thread, please reply to the thread with an update at least so we all know that you got the bug report.  Thx!

We are having the same problem with the preview version of Outlook since mail, website, and DNS are hosted by three different companies. 

What solved it for me is to click the the check box ABOVE the certificate tree labeled "Always trust ...".  Changing the value in the drop down boxes in the Trust section by themselves did not help.

Hope this helps,

   - Oliver

I'd noticed with the same Exchange account and upgrade on my laptop I didn't experience this issue so I've deleted and recreated my profile to see what differences there were.

Looks like under

~/Library/Group\ Containers/UBF8T346G9.Office/Outlook/Outlook\ 15\ Profiles/Main\ Profile/Data

there are old Mail Account and Exchange Account profiles that reference an obsolete shared mailbox. That mailbox had a from address on the sub-domain (xxx.mydomain.com) I'm getting the certificate warning for (it was testing at time of migration to office 365) but connection details and login were always via the main domain (mydomain.com)

Looks like the upgraded profile is doing something odd with these disabled profiles that from a user perspective are long deleted.

Hope that helps some in MS identify the cause - I don't want lots of confused users.

Hello everyone,

I'm still getting this error with the latest v15.10.0 (150508) release that came out in this week:

https://support.microsoft.com/en-us/kb/3048682

Here is the error (same as in v15.9):