If you're running antivirus software it might be worth disabling that & trying again.
Thanks everyone for your suggestions, its a really head scratcher and has me totally baffled. The webmail test emails go instantly and get received fine. However, that is not using any local mail settings on either pc or iphone/ipad and probably a different mail server at BT? When at work tomorrow I will try sending via a different WiFi (not my home one) possibly by a guest wifi we have at work and see what happens then. It might narrow it down further to what I think must be the problem, i.e. the router somehow.
I can't see it being the router. I suspect it is the mail server you are accessing when using your home wifi. Did you check if your public IP had actually changed when you disconnected for an hour?
@licquorice 'Did you check if your public IP had actually changed when you disconnected for an hour?'
Not sure how I would do that?
Either check on your hub Advanced settings > Broadband or simply type what's my IP in Google search
Ok, I have got my public IP now, so if I turn off the router for what 30 mins or an hour? How long does it take before it issues a new IP? Once back up online again, check the IP again and check it has changed. If it does not change, then what?
If it does not change give it longer. Do it over night when you are not using it if need be.
Try it as a straight reboot first. My router has the ability to momentarily drop & remake a connection in about 30s & I always get a new IP in that time.
Do you have an old router sitting in a cupboard to try? I also doubt it's the router but that would eliminate for sure.
@gg30340 Ok thanks for that. I just checked my IP and then just switched the router off for only a couple of minutes. Turned it back on and rechecked IP and the last three numbers have changed. I had tried that before asking on here and before contacting BT chat line, as its normally the answer to all IT issues 'have you tried turning it off and on', but it had not worked.
I just sent a few test emails as done previously, and this time they appear to have been sent and received as expected ...yahoooo! It looks like it has fixed itself this time. Whereas resetting the router to factory settings, powering off for nearly an hour all of which should have given it a new public IP. Don't understnd why but fingers crossed it fixed for now. Thanks for your time and help @gg30340 @licquorice @rbz5416