Certificate errors in Outlook office email client

I recently installed Microsoft Office 2021 on my laptop and migrated my Outlook .pst files over to it. Then I set up the Outlook office client to sync with, and pull my gmx.com emails to Outlook using IMAP.

This seems to have created duplicate folders in my account (sent, junk, outbox, etc) which I am in the process of going through and deleting.

But now I've also been getting certificate errors whenever I send emails. I've tried both answering 'yes' to continuing to use the server, and I've tried installing the certificate. Neither has stopped the certificate error messages.

Does anyone know how to fix this?

If you use a MS email account, it can no longer be set up as a pop or imap account.. MS announced earlier this year that by the end of the year we could no longer use their email accounts using any email app on any device (even their own) if we had those accounts set up as pop or imap which uses basic authentification. Users using these protocols began losing access 9/16/24.
That is addressed here. Ofc2021 does support modern authentification. You would need to delete your account in Outlook2021 and set it up again per option#2 Modern Authentication Methods now needed to continue syncing Outlook Email in non-Microsoft email apps - Microsoft Support

glasskuter said:

If you use a MS email account, it can no longer be set up as a pop or imap account.. MS announced earlier this year that by the end of the year we could no longer use their email accounts using any email app on any device (even their own) if we had those accounts set up as pop or imap which uses basic authentification. Users using these protocols began losing access 9/16/24.
That is addressed here. Ofc2021 does support modern authentification. You would need to delete your account in Outlook2021 and set it up again per option#2 Modern Authentication Methods now needed to continue syncing Outlook Email in non-Microsoft email apps - Microsoft Support

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Thanks. I didn't realize things had changed.

I need to read it over carefully, as I don't quite understand it at first glance.

So will I need to sync with Outlook.com from now on instead of my non-MS third party email: gmx.com?

Madrona said:

So will I need to sync with Outlook.com from now on instead of my non-MS third party email: gmx.com?

Click to expand...

I'm so sorry but I read your initial question incorrectly. For some reason I read you were using an @outlook email address (Don't know why when it's right there in front of my face) but I see now you are using @gmx email address.
My above posts relate to @outlook email address only so disregard it.

Since you are unable to install the certificate, that error is usually indicative of a server mismatch in settings.
Compare your settings to those in gmx articles here.
for imap- IMAP Server Data
for pop3 - Setting Up Outlook (POP3)

If that doesn't lead you in the right direction, I would contact your email provider. Explain your situation. They should be able to tell you the exact settings to put in Outlook2021.