Thunderbird is just a messenger; it sends messages from your IP address, using server configuration details that are provided by you, and reports messages from receiving servers back to you. I do recall a while back seeing a user being blacklisted from emails sent by Thunderbird, but that was due to an advertisement being embedded in messages by an anti-virus program. Thunderbird was just the unwitting carrier. With more information on the blacklist, someone here may have suggestions.

Was actually being caused by the Norton VPN.

Thanks for sharing that. I'll keep in mind in case we see a similar problem.

Have the same problem of IP address being blacklisted (by TB) not comcast. I can sign into comcast site & email with same credentials, no problem. TB gives me error message: "Temporarily Blacklisted IP address. Try again Later"

It's been 2 weeks and I've tried everything. Uninstalled TB and reinstalled it, went back to an earlier restore point on Win 10. Cleared Cache.

Don't have Norton antivirus. Only using Windows antivirus built in.

TB worked great for several years, now this.

Could sure use some help! Thanx Dennis

One solution I found was from Toad-Hall on 5/7/2023. It worked for me. I have found that comcast email burps from time to time. Since it's a secondary email I can let it go. My error occurred when opening TB and I re-enter the email address for the Comcast account. I then receive the message "Temporarily Blacklisted IP Address...try again"

The short solution was to enter ipconfig /release and then ipconfig/renew I closed TB and restarted the desktop before the renew. Check the links below. Toad-Hall provides a much better explanation with more detail and reference information.

BTW: I use Norton VPN. It was active with no problem in solving this issue.

Toad-Hall response: https://support.mozilla.org/en-US/questions/1410109

   Reference provided: https://www.xfinity.com/support/articles/releasing-and-renewing-ip-address 

This worked for me. Hope it works for you as well. -Dado

Sys: Win 11 Pro, TB Supernova 115.10.1