It sounds like your mail files are corrupted.

First of all, create a full backup of your Thunderbird profile.

Then 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 working 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

Also see http://kb.mozillazine.org/Keep_it_working_-_Thunderbird

Thanks for your response. Using Mozilla Backup I backed up the profile then opened TB and tried to repair the Inbox folder. It erased all the files in question. Ran the backup again to restore the profile and then tried to repair the Inbox folder. It again erased all the files in question. Do you have any other suggestions please? Thanks. Michael

Check you anti virus for the deletion or quarantine of a file called inbox.

The user interface is populated from an index file (MSF) in your profile. The display of the mail comes from another source. Anti virus programs a quite adept at deleting the whole mail sort for a folder to get a single "risk". The user interface continues to look good until you try and actually open the detail of an email

The second option is to open the inbox file in your profile in a text editor and look to see if the information from any of the emails is actually present (real corruption) but not displayed.

Thanks for your response. I have 148 megs in the inbox. Opening the folder in notepad brings up the text files, but to be truthful it would take me an hour to scroll through the messages which are a combination of text and apparently .jpg files. I contacted McAfee and of course they disavowed any responsibility. Given the abrupt increase in the number of 'spam' files blocked I have a suspicion that McAfee arbitrarily decided the missing files are spam. Unfortunately they gave me no info on how to retrieve or unblock the files designated as spam. I tried forwarding one of the messages to another e-mail address (mine). It did go through but the message is still blank. All my other folders are intact so I suspect the problem is with the 'Inbox' itself. If you have any further suggestions, it would be appreciated. Please keep in mind that I am not a whiz on figuring this out, so the instructions to me need to be pretty straightforward. I do appreciate your help. Thanks. Michael

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

Thank you so much for your time. I tried all the suggestions. Nothing recovered the blank e-mails. Every time I tried to repair the Inbox folder, it deleted the same 60 files, leaving about 60 files intact. I finally used an old Mozilla Backup file and recovered the emails up to the middle of 2015 and then sent them to myself leaving a net loss of perhaps 30 files.. Hell of a way to thin out the inbox though. I suspect it was a case of the inbox folder becoming corrupted (for whatever reason) as all the other folders in the profile remained intact. Have had no problems with my 2 other profiles. I suppose the moral is to back up your profiles on a regular basis. Thought I would have learned by now! You may consider this case closed and once again, thanks for your timely and informative help. Michael

I suppose the moral is to back up your profiles on a regular basis.

Indeed. See http://kb.mozillazine.org/Thunderbird_:_FAQs_:_Backing_Up_and_Restoring

You may consider this case closed

Good. Can you then mark the thread as 'Solved' please? Thank you.