Can't connect to IMAP using Mac OS High Sierra and Mac Mail app

Denis Gomes Franco

Well-Known Member
Sep 3, 2018
Tupã, São Paulo, Brazil
cPanel Access Level
Root Administrator
Hi. Today one of my customers said that he could not connect to his IMAP mailbox after adding it to the Mail app on Mac OS High Sierra.

I double checked every setting on this application (via TeamViewer) including TLS/SSL and IMAP/SMTP ports, to no avail. Also tried connecting non securely. It simply says it cannot verify the username and password. And the weird thing is: the Outlook app on mobile can connect just fine.

But here's a thing that might shed a light on this: Outlook 2016 on Windows was able to connect effortlessly, but only after throwing an INVALID CERTIFICATE error. That certificate says it was issued to "" (my hostname and domain of course) while I'm connecting to "", so obviously there is a mismatch - even though Cpanel correctly issued and installed an SSL certificate to "".

So, how do I resolve this?


Well-Known Member
Nov 20, 2014
cPanel Access Level
Root Administrator
I had the same issue about two weeks ago.
I updated our server to 8.0.14, and the very next morning I took a call from a MacBook user saying that his emails were not working.
He'd been previously working faultlessly for 3 years or more.

I found that disabling SSL along with secure password authentication allowed his email client software to connect.
At this point his emails started to come through.

I've no idea yet why it stopped working, however, I also suspect something to do with certificate errors.

see my other thread.

Remote MacOS user unable to retrieve emails


Staff member
Apr 11, 2011