Each machine that accesses the Internet is assigned a unique IP address for it to be identified. The error message you are getting is saying that the IP address that's assigned to your laptop is blacklisted. There are many web pages that show how to change the IP address. Unfortunately, I can't send a link or the message will need to be approved by a moderator and it can be delayed several hours.

Are you using a VPN? Because it could be the VPN that's making you look as having a bad IP address…

DavidGG, I'm not using a VPN. It's so frustrating that the only time there's a problem with this, it's only Thunderbird. Again, my BlueMail app is getting emails via the Comcast email address on my cell. This problem has corrected itself in the past and obviously Thunderbird continues to erroneously blacklist this IP Address on my laptop. I'm not a huge tech person so much of the terminology and processes are over my head. Is there just a way for Thunderbird to "UNblacklist" my laptop? Have had Thunderbird for so long that I'm loathe to change to another program but it looks like I may have to do so.

Thunderbird doesn't care what your IP address is nor does it blacklist anything. That would be a server thing and Thunderbird would be merely telling you what the server is telling it. You'll have to provide screenshots or reproduce what it is exactly that the error messages say, without paraphrasing them, in order to be able to figure what's going on.