This is not "gmails" behavior. This is called "verb" and it is one of the best things ever. I only use verb for signing up at stuff. So, i can sort, and know when someone misuses my mail address.
And, if i would need to create an alt, to post stuff, that i don't want somebody do bring in connection with me (TIFU, NSFW, whatever you like) i would use verb.
In theory, yes. You only need a Activitypub library and some lines of code.