The global search database still contains information about emails that: Either no longer exists Or the imap folder containing those emails has not been subscribed to be seen. Fix: Logon to webmail account via a browser and check to see if email is on server. If yes, in Thunderbird subscribe to see the folder it resides in. Or if gmail, email may be archived. Fix: Logon to gmail webmail account via a browser and check the 'All Mail' folder. Gmail will archive all emails in the 'All Mail' folder if all labels were removed. Move email to a folder that is imap accessible to apply a label and make sure you are subscribed to see that folder. Or you are operating in offline mode and the emails in imap account folders have not been fully downloaded. Fix: return to online mode. Suggest you rebuild your global database to ensure it is up to date. * https://support.mozilla.org/en-US/kb/rebuilding-global-database