IME: I’ve never had anyone remove it (although some don’t accept it and others will have bugs that result in an unusable account if you register with it.) I used one with the company I most recently interviewed at (they used a third party service for the HR site and I’ve had trouble with sites like that selling my email address which is just so enraging honestly.) Every. Single. Time. I logged in to fill out a form after getting hired I had to call HR and have them reset my account because of some weird bug.

Though similarly, email usernames ('local part') are case sensitive but I've never encountered a mail server where this was the case. I imagine if a nefarious party stripped the markers, they'd lose the tiniest percentage of their audience that way.

(Aside: Your own approach to using + is quite clever as it's the total opposite to most users, so you'll see who pulls this trick ;-))

Several email providers treat a + symbol as the end of the first part of the address and ignore everything between it and the @.

I think the responder’s point was that analytics providers just ignore things after a + too