This is a bug that is tracking this

• Bug 565171 - The RETR command did not succeed. Error retrieving a message. Mail server plus.pop.mail.yahoo.com responded: problem retrieving message.

There is no fix, but there are comments that say that switching from Yahoo POP to IMAP4 helped with the corrupt email messages.

I DO NOT use YAHOO!!!!!!!!!! Your answer is of no value!!! There is a problem with Thunderbird in that it will not ignore a bad email header and will not continue to download valid email messages. Thunderbird should display the "bad" header and allow the user to delete the email message. This would allow the user to continue to have access to their email message without having to contact the email server provider to wait 2 or more days to have them delete the bad message header.

PLEASE FIX THIS PROBLEM AND BE SUPPORTIVE OF YOUR USERS!

Ok, I understand the situation. There is no easy way to do this, and the work around is an idea, as I do not have corrupt messages to test with.

If you put them in a folder, would repairing the messages in the folder work temporarily, then you could move them back? http://superuser.com/questions/416852/how-can-i-force-thunderbird-to-re-do...

Right click the new folder after creating it on the webmail, right click on the folder, select properties and synchronization, download now. See if the messages download in the folder with the corrupt header.

This is a bit adhoc.