Outlook 365 on Exchange 365 user config constantly pops up with certificate error

Copper Contributor

Morning Everyone, 


Im hoping someone can give me some guidance on this as I am struggling now. 


We have a company we support who are on Exchange online with office 365. Prior to this they were on hosted exchange and then prior to this (upwards of 5 6 years) they were on on Premise Exchange. 


Since some updates to office 365 apps one of our users is no longer able to use Outlook for emails.  When she tries to use it she is continuously getting an expired certificate pop up and its not allowing her to open outlook. We have noticed that this pop up comes up in other versions of outlook (2016) but when you click on ok it goes away and then tries to load the office 365 logon and then works. 


I suspect it has something to do with an old exchange object in the server somewhere but im at a complete loss as to where.


Any help with this is appreciated. 


Below are the things I have tried :- 


* We have tried forcing her machine to ExcludeScpLookup = 1.  We have enforced by group policy and locally on the machine to no avail.  We have also tried to exclude the other autodiscover lookups (can't remember them at 

* On the DC i have check ADSI and cannot find anything to do with exchange in there

* On the DC IIS was not installed but I have installed to see if there is anything in there that I may have missed

* On the DC I have checked DNS and there is nothing that I can see that may be referencing an exchange server but happy for some guidance on this .

* On the Domain Holder DNS the CNAME is correct for the autodiscover it goes to autodiscover.outlook.com for office 365. 

* We have also gone through all the expired certificates on the server and marked them as "Disabled for everything" and then rebooted the server last night. 


I am at a total loss now and any advice is appreciated. 


The exchange server that was on there may not have been decommissioned correctly in the past.  Im not sure what was done as I was not here then. 

2 Replies


Try installing the Microsoft 365 certificate on the problematic PC!


Microsoft 365 encryption chains 

Thank you for your input.

We are just waiting to test on the machine in question.