Certificate Error

Bronze Contributor

Couple of my users are receiving this error for outlook.office365.com in Outlook 2010.

Any ideas?


14 Replies

Hi Cary,


There is an Hybrid implementation ?


What the certificate says when you click on "View Certificate" ?

No, it's not Hybrid.

I didn't get a screen shot of that unfortunately.





Ok Cary, 


If the problem presists, please take the screen shoot to see the certificate.



This is common erorr if you do not have the SSL certificate by compelete FQDN of destined client domain/server. Example: server1.contoso.com.


Try fixing the name of the certificates in your environment/office365 connection. Infact you have to improt new certificate from CA authority server in your environment. 


Hope this helps you to fix the issue at your IT environement. 

Why would I need a SSL certificate when I'm connecting to outlook.office365.com?

Our Autodiscover CNAME entry for our domain points to autodiscover.office365.com. All of our mailboxes are in Office365, none are on-prem.

You sometimes see an certificate error when connected to (for example) hotel wifi, whoch terminates ssl connections



I am assuming you have recently migrated to O365. Please get users to run this O365 diagnostic tool which will  pick O365 certificate and create outlook profile. https://diagnostics.outlook.com/#/  if they have  O365 valid exchange subscription plans. 


Alternatively you can also use this tool for Office 365 Desktop Setup Tool for Office 2010 and Office 2007  https://www.microsoft.com/en-us/download/details.aspx?id=50360



Also look this KB https://support.microsoft.com/en-gb/help/3007582/certificate-error-message-when-you-start-outlook-or...

Please let me know if this solves issue.  

No, our email has been in Office365 for 2 1/2 years now.


We haven't seen the error since it first occurred so I'm going to pressume it was a temporary error on the server side.

Up to you but would recommend to get users with older version of outlook to run this tool to get latest updates from 365. https://www.microsoft.com/en-us/download/details.aspx?id=50360


Been O365 Support Engineer, we had few customers having issues. 

Our Office 2010 is already up-to-date.

We had a DNS server (small-office router actually) apparently corrupting DNS lookups – I suspect because the record Office 365 returns is rather large, what with multiple addresses and IPv6 addresses. Outlook was presumably thus sent to an adjacent server in the Microsoft server farm. Certificate errors was the error there. It would be interesting to see what server names were allowed by the certificate.

Looks like a proxy certificate issue. Especially, if users connect to internal source (e.g. SharePoint) and Office 365 using Outlook.


We have a couple of clients with this error.  They have two different Internet Service PRoviders, one active and one of backup. Booth customers had the same ISP active, we change to the backup ISP for all out connections.

We check DNS, SPN, outlook´s updates, etc..

The issue was fixed changing the ISP .


HI cary!
Trouble to confirm whether all users have this problem。
If it is a few users, reconfigure Outlook is resolved!