Hi Not that this helps much - but I tested this and the original email remained in Inbox. Created tasks and events - email was still in Inbox. Deleted all events and tasks created from email. Original remained in inbox. Closed and opened Thunderbird - email remained in Inbox. So, in my situation, Windows 10, with Exquilla, Thunderbird did not lose the original message. Could it be something Mac-related? Agnes

gstlouis1 said

When you convert an email to an event by right clicking and selecting either convert to: event or tasks. Does this email disappear? Because I have been converting emails to events, then when I got back in trash or inbox to lookup the history of that email I can not longer find it. Which kind of sucks if you had a long conversation going and can't remember everything...

I am Using TB 68.3.0 (64-bit) on MAC OS X 10.12.6 - I can create an event from messages and the messages are still in the Inbox.

Be sure you have the latest version (68.3.0 (64-bit)) of TB, and then try rebuilding TB Gloda , or "Global Database" ... as per the instructions on this very helpful page: https://support.mozilla.org/en-US/kb/rebuilding-global-database

There is a chance that the missing messages will be back after you do this. Otherwise check in your ARCHIVE Folder to see if they are hiding in there.