Thunderbird email client - Caot delete email messages in 16.04

I seemed to have fixed - first tried to go into account settings - disk space and setting it to delete all but the last 20 or so messages. It did this but still didn't delete.

But I then deleted the account - uninstalled - reinstalled (this kept my other account so must be stored in a hidden file) and set up my account once again, but this time it only loaded the last 50 or so messages. Now deletes OK.

It might be something I have done - might have used the wrong server address when I set it up eg virgin.com which loaded the mail - but anyway it's fixed for me.