I have had two email accounts for many years, both on my iPhone 7 (IOS 13.5) and on my Mac (Mojave, OS 10.14.6): a gmail.com one and an iCloud.com one. I used also to have a Btinternet.com one on each device, but abandoned the BT accounts a long time ago because of continual problems. Recently BT has modified and, seemingly, improved its email system, and I decided to reinstate the BT accounts on both devices. As soon as I started the procedure of adding a BT account on either device, I was told that either my password or my username is wrong. Yet the identical password and username allow me to access my BT account — and my emails in the form of webmail — without any difficulty. They are therefore obviously correct. I have had a lengthy correspondence with a very helpful technical person at BT, who confirmed that my password and username must therefore be correct and the problem must lie with my attempted settings on my two devices. I have checked and rechecked these with the help of documentation supplied by BT, with no success. Finally I temporarily unchecked Mail and Notes in System Preferences/iCloud on the Mac so as to prevent any interaction between devices and tried setting up the BT account on each device yet again, but with no more success than before. Any advice or help with this depressing situation would be very much appreciated.