Mail on Big Sur cannot verify server certificate for mail.twc.com

Cannot verify the identity of the server "mail.twc.com" - Server certificate invalid?

For the past week+, have been unable to download any of my Road Runner (RR) email's from Host : mail.twc.com. This event was sudden, with no warning, and it's Not my Mail client as I have AOL & Yahoo email accounts that work perfectly, for over the past 15 years.

In June 2026, installed the Security Update for Big Sur 11.7.10, now, 11.7.11. During August thru September, started having issue’s with Email’s downloading, so per Protocol > Changed PW & Removed / Re-installed RR email account. Mail ran like a Swiss watch, until October, when the “server certificate is invalid” notice started popping up ... up to now.

All anti-virus/spam apps, and, vpn are offline/paused, but, didn’t make any difference. Zero.

...

ISSUE 1 - The certificate in question is > GlobalSign Root R46 (see image), and is Not listed in my Keychain list. Note - have two TWC / RR accounts, and have been accessing them via Spectrum webmail, at least over the past 3 to 4 weeks, FYI.

Last week, I did spend over an hour, with a Spectrum tech Tier 2 support, in Texas; however, he was unable to provide a Solution.

Note - the GlobalSign Root R46, does NOT offer any options to Accept or Trust it.

...

ISSUE 2 - Spectrum webmail has Turned Off the "Forward Email" feature, without Notice, so that was surprising for the Spectrum cohort with TWC / RR accounts. This is a great example of a system event when having that option, would have been at least a Plan B solution.

iMac 27" / Big Sur 11.7.11 / Mail 14.0.x

Thx ...

Posted on Nov 6, 2026 3:19 PM

1 reply

Luddite61

Level 1 (8 points)

Nov 9, 2026 1:25 PM in response to DSM808

Having same problem with my Mac desktop, running Catalina. I was getting a ton of bounced emails because over memory limit, went into Spectrum Webmail and cleaned out a bunch of old garbage, my email resumed working fine on my phone and tablet but no longer works on my computer, the command to get mail fails and I get the message that Mail can't verify the identity of the server "mail.twc.com." This happened mid-October, not sure if the two incidents (the bounced emails and the failure to download emails) are related or just coincidence?

Wondering about trying the suggested fix to remove and readd the RR email account, but if I do that, will I lose the cache of existing downloaded emails that I'm holding in my inbox in Mail? And per your experience, is this likely not going to help?