Just to make sure, are these emails not appearing in the inbox folder but elsewhere in Thunderbird or not appearing in Thunderbird at all?

Thanks Ben. I know the emails are there because when I do a search they come up, but where they are, is the mystery. I notice one of the emails is a response from a BCC batch so would this hide them from being individually listed?

I know the emails are there because when I do a search they come up, but where they are, is the mystery.

If you search for the subject of the email exactly, does the "Folder" section on the left sidebar reveal where the email is? They should be in the same folder as they are in Outlook.

In my experience, Thunderbird occasionally begins to misbehave when upgrading the same installation to later versions. At this point, I would recommend starting fresh with a clean Thunderbird profile. If you decide to perform this, please keep a backup of your existing profile for safe keeping. I can attempt to locate instructions on how to perform both tasks if needed.

I notice one of the emails is a response from a BCC batch so would this hide them from being individually listed?

No, BCC only conceals the recipient('s) email address(es) and not the actual email itself.

Hi Ben, Chris1 sent a suggestion of repairing the folder, that may have done the trick. Thank you for your support. Regards Alan

Glad to hear your problem is solved, Alan! Would you be able to share the instructions on how to repair the folder here in case someone else runs into this problem in the future?

I have exactly the same problem but only with mails from one particular organization, when I do a search I see I have 34 mails but it only shows 5 emails. I've tried the repair option but nothing happened.

Any other solutions ....??