I don't like to solve any issues with software or hardware. But some days ago in our office we installed MS Outlook for iPad, but unfortunately we normally used it only 1 day. Next day all the messages we received were disappeared. Now we can't extract those important messages, is there a variant?
This isn’t a great answer so please forgive me in advance…
1) Check that webmail works ok - log-in here if there are any account issues you will get an error of one sort or another - follow the advice there - assuming all is ok carry on reading.
2) Try a different email client - As far as I can tell, Outlook for ios/android (this is not the same as the Office Outlook product) doesn’t operate like a traditional email client, their app seems to connect to Microsoft’s own servers which then connect to the mail service you have configured – I haven’t proved this yet but it seems to be the case - I’d suggest trying a different email client and if that works then you will know if it is the Microsoft servers or BT servers causing the problem.