Do you also have a smartphone app which is possibly set to delete mails after 14 days?
Not that I can see. What app might it be?
Whatever app you use to read your mail on your phone.
OK. Can't see anything on there to suggest emails are automatically set to delete after 14 days
This looks like the same problem as message 413 on the Feedback thread https://community.bt.com/t5/Email/BT-Webmail-Feedback-v2-post-16th-April-release/td-p/2376642/page/4....
The question is, are the emails being deleted or are they just inaccessible?
Sadly I don't know the answer.