Certificate error in Outlook 2016/365

I have checked the Internet for a solution for this problem, tried a few, but none works.

I recently bought a new Windows 10 Home computer for my wife and installed Outlook as part of our Office 365 subscription. The new computer came with McAfee LifeSave Antivirus/Firewall. Whenever my wife opens Outlook, the following message appears:

After she clicks on "Yes" everything works fine, but the pop-up message is annoying. I temporarily disabled McAfee, but the error persisted. On her previous computer with Windows 10 Home, the problem did not appear.

Her IMAP connection uses port 993 SSL/TLS encryption.

Her SMTP connection uses port 25 with no encryption (although I have also tried it on a different port with encryption).

I use Outlook on a different computer without this problem.

Any solution out there?

You did not include the error message.

Windows 10 includes a firewall and antivirus. You don't need a third-party add-on. If the error mentions McAfee at all, then were I you, I'd rip it out and throw it away. It may be installing an extra trusted certificate that does nothing more than provide an extra attack point to bad guys. There have been so many reports lately of security programs that add certificates giving attackers a foothold.
Brian

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What does the text of the message say? (The image didn’t make it. )
Diane Poremsky [Outlook MVP]
Outlook Resources: https://www.slipstick.com
https://www.outlook-tips.net


** I don't work for Microsoft, I just volunteer here.**

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The message says:

"The server you are connected to is using a security certificate that cannot be verified.

The target principal name is incorrect."

Then comes a button:  "View Certificate".

Then the message continues with "Do you want to continue using this server?"

Followed by two buttons:  "Yes"  and  "No"

Hellmut

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If you are using your own domain name and are using something like mail.yourdomain,com, try the service's general server name (ie, for godaddy they are imap.secureserver.net and smtpout.secureserver.net). Or you can try one of the solutions at https://www.slipstick.com/outlook/security-warn... - adding the IP to hosts file is popular.
Diane Poremsky [Outlook MVP]
Outlook Resources: https://www.slipstick.com
https://www.outlook-tips.net


** I don't work for Microsoft, I just volunteer here.**

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>> I use Outlook on a different computer without this problem.

Also, check the server names you use on that computer - try the same ones on the new computer. They re in File, Account settings, double click on the account.
Diane Poremsky [Outlook MVP]
Outlook Resources: https://www.slipstick.com
https://www.outlook-tips.net


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I use the same server names on my computer, "mail.golde.org". No problems with the certificate.

Hellmut

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The certificate is for the name mail.golde.org? The error usually indicates its a shared server and the certificate is in another name.
Diane Poremsky [Outlook MVP]
Outlook Resources: https://www.slipstick.com
https://www.outlook-tips.net


** I don't work for Microsoft, I just volunteer here.**

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Hello,


I suggest completely unistalling McAfee I have seen many cases where it is in conflict with Microsoft Office and causes many issues. Windows 10 has antivirus software which will protect your PC.
More info about Windows defender here: https://support.microsoft.com/en-us/help/17187/...
After uninstalling restart the PC and test the Outlook connection again.

Regards,
Manuela

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I have solved the problem for now by using unencrypted communication for my email. That is probably not a good idea in the long term. Any thoughts on that?

Hellmut

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It depends on your needs and concerns, but yes - I would rather suggest to try removing the McAfee software. I think that the risk in that case is lower. Or at least you can try the connection from anothe PC which doesn't have that antivirus.

Regards,
Manuela

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Last updated September 30, 2020 Views 19,457 Applies to: