Forgot to mention that my other account is working fine with the same settings.

That sounds like a long running Nortons anti virus issue, but any anti virus can do it really.

Disable the email scanner and let that message actually download completely. Once you have your mail you can turn the scanner on again if you wish.

Matt, I have Panda AV, part of McAfee. I can't seem to find any tab in that program that lets me turn off email scans. Would it be in Thunderbird?

Btw, this one email keeps on coming, over 100 copies and still not stopping!

McAfee and Thunderbird have a very rocky relationship, going back a number of years now. I do not know if Panda is "same same", but we have some instructions for McAfee at the link.

https://wiki.mozilla.org/Thunderbird:Testing:Antivirus_Related_Performance_Issues#McAfee

In looking I did locate this http://support.pandasecurity.com/forum/viewtopic.php?t=5481&p=23656

So based on that, try the two options.

Av off, process monitor off. You are obviously connecting, so I see no point in trying with the firewall off which it the third option discussed there.

Before I uninstall my AV (there is no obvious way to turn anything off, it's a free version), let's review: I have two email accounts with settings same same. Both use Thunderbird. The cascadebuilders account has no issues with receiving, so why would AV mess up only the one account? I think it has something to do with the only message that has been able to get downloaded every time I click on Get Messages. I have received more than 100 of that same message and it's still happening today. It seems like that message is stuck at the head of the queue and creates a problem.

If you are talking about a POP mail account: Log on to webmail account using a browser Delete that email off server or move it to another server folder. If you cannot see it in Inbox, it might be in the Spam folder. Please empty the Spam folder anyway.

In Thunderbird Try GetMessages to see if you can download more emails.

Report back on results.

So, I opened Microsoft Edge and went to my yahoo mail account, downloaded the 150 or so messages without any trouble, deleted them with a few exceptions, then went back to Thunderbird and viola! the remaining messages downloaded quickly without any trouble. I suspect there was a corrupt email in that batch that would not download to TB, but thankfully would to E.