Problem with btinternet email being offline on Apple devices so not sending mails.

I have recently been unable to send emails on my iphone or macbook through my Apple mail app. I can do it within bt.com, but not Apple devices.

When I contacted Apple I was asked to delete my btinternet mail on my phone and try and re add it. This was not possible and the apple chat was halted saying the fault was with SSL/TLS and to contact BT.

BT tried and despite me resetting my password several times, they were unable to help and could not find a way to get my mail to come through any Apple device and to make the outgoing server online. I am able to send and receive emails through BT.com. Please can anyone assist how I get my mail back on my iphone and Macbook