I'm using the Windows 10 Mail app with my personal IMAP-server using SSL, using an internal corporate CA Certificate (SHA256, trusted as Root CA by the clients), and a wildcard-certificate on my connection (also SHA256, mydomain.com and *.mydomain.com).
This formula worked like a charm for the Windows 8.1 Mail app, and still works perfect in Outlook 2013. Also Edge, Chrome and IE trust the wildcard-certificate perfectly without issues.
Only the Windows 10 Mail app complains that the certificate for imap.mydomain.com is invalid and refuses to collect or send my mail. I can push the button to collect mail anyhow, but the error keeps recurring and the app won't send any mail.
Translation from Dutch dialog:
The certificate for imap.mydomain.com is invalid.
This can indicate an attempt to gain access to or theft of your data.
It's not recommended to connect to this server.
Do you want to connect anyway?
I once got the error code 0x80072f89 to appear, but can't really recreate that, so I'm not too sure this actually was 100% related.
Can anyone tell me how to fix this? Or how to debug the reason for certificate denial. Or point me into the direction to find what specific requirements exist for imap/smtp-certificates for Windows 10 Mail?