iOS 11 mail SSL issues

I had the same problem. (Approximately) after update to beta 2, one of my IMAP-accounts stopped working because of an SSL-error. The logfile on my OS 11 device told my about trust-problems (didn't save the logfile, sorry).

I suspected that it might have to do with the certificate of my mail server (I was still using a StartCom certificate; StartCom was having trust problems with the big IT companies recently). I exchanged the certificate and ... it is working again.

So, please check whether you cert is no longer trusted.

I have the same problem and also with a StartCom certificate. The certificate checks out as Good with the Certificate Assistant and the email accounts all work fine in Sierra and iOS 10.3. It also checks out as good at sslshopper's ssl-checker

My certificate uses an intermediate certificate – StartCom Class 3 OV Server CA. I wonder if the new validating system isn't handling intermediate certificates properly.

smschaef, was your certificate from StartCom? Did it involve an intermediate certificate?