When I opened my email, some messages were unreadable or only headers (no text in message). or mismatch with header
When I opened my mail this afternoon and looked for new messages received in the previous hours, I found that they were unreadable garble and some didn't have any text in the body. I went back to messages from earlier today (that had been fine) and found the same situation. I then looked at messages from prior days and saw that messages from 8/11/15 8:20 a.m. until 9/17/15 2 p.m. were affected. Ones before 8/11 and messages received later this afternoon were fine. What can I do to restore the missing messages?
Opaite Mbohovái (1)
It sounds like your mail files are corrupted.
Try to rebuild the index file of the troubled folder. Right-click the folder - Properties - Repair Folder
Note: depending on the corruption this may erase messages from the affected folder which cannot be recovered anymore. In that case you'd need to restore them from a recent backup.
Corruption is often caused by anti-virus software messing with Thunderbird mail files. It is therefore recommended to create an exception for the Thunderbird profile folder, so that the real-time scanner won't attempt to scan the profile with your mail.
For more information on the profile location see http://kb.mozillazine.org/Profile_folder_-_Thunderbird
Moambuepyre