Apple Mail changing my send from email address
I've recently changed my primary email address from the one I've used for years. Even though I select the new email address in the "From" section, and have made my new email address the default "Send From" account in Apple Mail settings, after I press send, Apple Mail is reverting the send from email address to my old email address. It is doing this on my MacBook and my iPhone.
How do I get Apple Mail to stop automatically changing the send from email address to my old one?