Your email client, whether Thunderbird or another, does not cause blacklisting; that happens from content of messages or inability to confirm sender. The specific error message may help you in assessing the cause of the blacklisting.

There are two different message windows that pop up when I attempt to open Thunderbird email via laptop. First message states: " Login to account XXXXXXX@comcast.net failed. Login to to server imap.comcast.net with username XXXXXXX@comcast.net failed." Window offers options to "Retry", "Enter New Password", or "Cancel". Second message appears at lower right corner of screen from Thunderbird states, "Alert from account xxxxxxx@comcast.net: Temporarily blacklisted IP Address - try again later." The Comcast email on my droid phone finally reopened for a while yesterday but then went back down again about 15 hours ago. (I hadn't done anything to fix emails on the phone... it just happened itself.) That message states that the "Sync failed" so emails are, once again, not coming through that source either. Email on phone is not Thunderbird account.

have you pursued this with Comcast? If phone and PC can't access messages, it seems to be a Comcast issue.

Solved the problem. It was not the server, Thunderbird, or Comcast. Since I was unable to access any emails, I decided to clean up/delete/trash all unused ads in email feed. (Kept the necessary emails.) Must have cleaned out almost 3,000 of them. Looks like it may have been a memory issue? After cleaning out the Inbox and emptying the trash, emails began coming in dating back to May 22, 2024. Problem is now resolved. Am receiving emails on laptop and on phone. Will now do a better job of keeping up with removing the garbage emails on a daily basis so that this doesn't happen again. Thanks David for your input.

Thanks for the update. After all that, please be sure to do a backup of the profile. best way, in my opinion is to: - exit thunderbird - copy c:\users\<yourid>\appdata\roaming\thunderbird to external media

I also suggest viewing the profile from FIle Explorer, as there may be accumulated clutter in the profile, such as multiple copies of prefs.js file and multiple copies of accounts. That doesn't keep Thunderbird from running, but does cause profile size to keep increasing.