And, as mysteriously as it started failing... after a day, it has just as mysteriously started working again! No idea why, perhaps it was something on the provider's end. I just hope it continues working!

[I've been using Thunderbird for years (Windows 11 PC), and all has been working fine as recently as last night. Starting this morning, I continuously get the error message, "Login to server mail.comcast.net ]

2025/11/26 I have same problem only with with CompuServe.com email.

Please advise...

Good snowy morning, all! I have this issue, too, now for the second time. The first time was 11//10/2025 for roughly a 1 to 2 weeks. Spoke with comcast/ xfinity on 11/13/2025. Started mysteriously working again several days later, some time the following week. Then last Thurs., started again through this morning. Have tried all of the xfinity things. They says it's Mozilla/ Thunderbird. Our Thunderbird is updated fully; using Windows 11 Pro, Lenovo Yoga 7 laptop purchased 2025. Please help as soon as possible. Thank you and God bless!

I continue to have this issue, and I'm certain it's not a Thunderbird problem. After many calls to various levels of Comcast/Xfinity support, I was told that my IP address was on a couple of blacklists. One blacklist they got me off of immediately, but the other they said could take a week, and there wasn't anything they could do about it.

For the details, first I got my IP address (I used whatismyip.com). Then I went to www.mxtoolbox.com, clicked the box for "Blacklists", then entered my IP address and clicked "Blacklist check". It revealed that my IP was on two blacklists: UCEPROTECTL2 and UCEPROTECTL3. From what I can tell, I am on these blacklists not because of my specific IP address, but because my provider, Cox Communications, has subnets that have been associated with spamming, so everyone with these subnets (which I evidently have) gets blacklisted.

I guess my next step is to take it up with my provider, Cox, to see if they can do anything about it or perhaps assign me a different IP address (which of course may also be comprised).

I see all the previous problems are 2025. Mine just happened 03 26 2026. Been using Tbird for many years,no issues. Doing research, MS windows 11 update seems to be the culprit. BTW, I am running a Dell laptop , Windows 11. My problem is trying to log in to Thunderbird , xfinity server won't take my password (Comcast email). Everything was fine until I installed "Win 11 update 2026-03 KB5085516 26200.8039"

So , I uninstalled the MS update, but the problem continues. Not sure what to do next !