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Old 08-30-2019, 03:50 AM
Traveller99 Traveller99 is offline Windows 10 Office 2013
Join Date: Jan 2016
Posts: 7
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Default Outlook (in Office 365) Certificate Errors

I recently reset my Windows 10 PC, ie reloaded Windows and re-installed fresh copies of all software. Since then, Outlook produces certificate errors when I connect to any of my email accounts. These accounts, all set up as IMAP, are with btinternet, and via two websites that I administer on different servers. I am using I/C port 993 and O/G port 465 with SSL/TSL selected. SPA is not used. These settings were populated automatically when I reconnected to the accounts after resetting the PC.

The error is "The server you are connected to is using a security certificate that cannot be verified. The target principal name is incorrect." If I click "Yes" in answer to the question "Do you want to continue using this server?", the accounts all work normally.

I have read everything I can find on forums etc, reviewed all the settings and investigated all the suggested solutions. Nothing has prevented the certificate errors from occurring. I have also checked all the port settings etc for the various accounts against those used on a Windows 10 laptop which does not produce any certificate errors when connecting to the same accounts. This seems to suggest that the problem lies with my freshly reset PC.

Can anyone please offer any advice?
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