How do i udate a certificates for apple mail on iso14

So I ended up just deleting the account and reinstalling it. After a reboot, I got the same not trusted notice, but clicking Details this time brought up the dialog that this time allowed me to Trust the certificate. So reinstalling the account worked.

Thanks Old Toad, for the reply. I use Apple Mail and Network Solutions for my email client. However, I did manage to find a certificate just a little while ago, that I could "trust" in the Keychain. It immediately got the email downloading onto the iMac desktop computer. So that is fixed.

And sorry about the confusion using ISO when I meant mac OS for iMac.

I am having the same problem with my iPhone Xr that is on iso 10.14.6. I just updated to this, but I had this same problem with the previous version - that's why I updated, but it didn't fix it. When I get the "Cannot Verify Server Identity" dialog, I click on Details and it tells me the certificate is not trusted, but selecting "Trust" in the resulting dialog box is not possible. It is missing from the header where it used to be. There must be an easy way to update this certificate on the phone, but I can't find a way to do it. Much appreciate anything you can offer.

David G