Rebuild of msf does not complete

I have a folder that is 188 MB. When I open Thunderbird, it rebuilds that msf file it tells me that I only have 27 messages in the folder. I know that there are a lot more than that.

I have tried deleting the msf file and restoring it from a backup. The msf for the backup file rebuilds with only 27 messages as well.

Is there a way to get the entire folder back or is it a total loss?

Thanks

Janene