Right-click the folder, Properties, Repair Folder, and see if that fixes it.

Thanks. I tried your suggestion. It changed the subject line and time stamp of the corrupted e-mail from the friend to that of the newsletter. The content was unchanged and the original message is now gone completely. It does not show up in the Trash or Spam folders.

I recovered the information by asking the friend re-send it but I am concerened about this happening again and not being able to recover something important.

Error

If a folder repeatedly shows this kind of corruption, it should be rebuilt according to these instructions. To minimize the chances of this happening, keep the Inbox as sparse as possible, compact folders regularly, and do not allow antivirus apps to scan email (add the TB profile folder as an exception or exclusion). And, make regular backups of the Thunderbird folder, as it is the easiest thing to restore. Its default location in Windows is:

C:\Users\username\AppData\Roaming\Thunderbird

Thanks, will try.