I have had this lack of interest from bt as well- just blaming my clients when it's a server issue. Not evryone wants to do webmail or imap! I use OEclassic and it has been fine for years. I unplugged the hub overnite and it seems to be sending again now- but for how long? BT need to get a grip, no good thinking they can fob us all off, and that we know nothing!
For months I have not had this problem, but this morning it returns! No change to any setting in Outlook or anything else on my PC - broadband is all up and running OK, so where is the fault? Can only assume somewhere deep in the BT servers which they will never admit to. Only solution is to wait and see if sometime in the future it just magically rectifies itself. Meanwhile have to log in to Web Version of BT mail. I really do not have the time to waste on even reporting this issue anymore. It's something BT should be monitoring proactively and apply the fix as and when they are aware of it. If a TV channel encounters broadcast issue it normally transmits an apology notification.