Okay so you can proxy via Apple as well as choose from [email protected], [email protected], or [email protected]. What if you want to be [email protected] today? In Thunderbird, you click on the From field and change the name, et voila. From the comment above, I presume that on macOS email, you will need to dig into settings.

My use for this is to give everyone a unique address ([email protected] is one that was leaked to spammers already anyway). I block senders that send spam. No need to ever wait for spam filtering or check any spam box, because I get spam on maybe three addresses per year and those are easily dealt with

(Of course, your email server will need to allow using arbitrary sending addresses.)