Does the account fall into any of the categories listed here?

https://support.mozilla.org/en-US/kb/thunderbird-android-import#w_not-supported

Hello and Thank You.

I had checked that page before and my inbound is POP and outbound is SMTP. I can send screen grabs of the setup if you wish.

I am pretty well technical and worked in Telecommunications and IT from 1978 to 2003, so you can ask more difficult questions if needs be!

Regards, Simon.

Post the name of the mail provider. In the meantime, you can just add the account manually to TB Android, as the export only includes server settings and passwords. On my setup, the export recognizes a POP account, so it isn't restricted to IMAP, although the vast majority of users with accounts on multiple devices, especially mobile ones, will have IMAP setups.

Thank you, that is most helpful details appended in screen snaps (png). Rgds, Simon.

IONOS is a fairly common provider, but I've no idea why the export fails. There are a couple of places that discuss these issues, but I wouldn't be too confident that either one would offer a solution:

https://thunderbird.topicbox.com/groups/android-beta

https://bugzilla.mozilla.org/show_bug.cgi?id=1918537