Getting Mail to communicate with BT Yahoo
I'm trying to get out of a Catch 22 situation. Having changed my password on BT Yahoo I now cannot access my emails through Mail on my iMac. I can only access them on the BT Yahoo website and on my iPad. I have been talking to Apple support from 8.00 am to 2.00 pm today and they have concluded that the problem is with BT Yahoo and that I should contact them. I have done this and after 2 more hours BT have told me the problem is with my iMac. They say the problem cannot be with them because the email works on my iPad. The same thing happened in early April and was solved by Apple but now they say there is nothing more they can do. I lost track of what the Apple advisor was doing but accounts were deleted and reinstalled to no avail. They reset the iMac to factory settings with no joy.
I really don't know what to do next, hence my posting on this site. Any advice?
iMac 27" 5K, macOS 10.14