What is your account type, POP or IMAP?

Account type is POP.

With POP those 235,000 messages should already have been downloaded to your computer - please confirm.

In that case, login to your account via webmail and move those 235,000 messages to a different folder on the server, or simply delete them.

Yes, the 235,000 messages have been downloaded to my computer, through March 7 @ 4:25 pm. Normally I would open up Thunderbird and it would show that I have 637 messages to download, or whatever the actual number is from March 7 forward. That's why my original question was how Thunderbird lost track of the messages it had downloaded and the new messages to be downloaded and how that could be fixed.

I have thought about going through the manual deletion of old messages, but, in order to keep my new messages, there are over 4500 pages of old emails to delete. But since the server crash, it can take at least a minute to display one page of messages. And 75% of the time it ends in an error.

I have tried talking to TimeWarner customer support, but the person answering the phone only takes messages and tells you a Tech will call you back. I haven't been able to talk to a tech in 6 years.

Sorry for venting and I do thank you for your help.

Thunderbird has not lost track of your messages. but in the recovery process your provider has changed their index numbers so Thunderbird asks to continue and the reply is as you see, because while you and I may see those mails as the same computers do not. new number = new mail.

So really you have only two options.

Move them as already suggested, or let them download. This time you might change the settings so Thunderbird deletes them from the server when they are downloaded so this does not happen again.