Right click the folder, select properties and then the repair button. That will rebuild the index to the account and hopefully your mail will appear unscathed.

I did that and it made matters worse: the list of emails inthe Inbox also disappeared.

So the reindex can not find any mail to index. Has your anti virus program found any email borne malware, or identified anything it has put in quarantine (like your inbox)

Yes, it did find some infections and decided it was going to clean them. Is this what is likely to have caused the problem? Thank you for your postings and desire to help: much appreciated.

It is a distinct possibility, but you will have to look through quarantine and activity logs for your anti virus for a file named inbox.