sender email address was not valid
I have this problem. Apple have had the problem for at least 10 years! I have an iPad proc, a 2020 MacBook Pro and an iPhone XR. I can receive from the iPad and the MacBook but cannot send from them. However I can both receive and send from my iPhone. I have deleted accounts and re-added them and all the boxes are ticked. Whats going on Apple?
iPad Pro, iPadOS 13