If someone doesn't want your emails they'll have almost certainly put a Block Sender on them, so they won't get through. So there's really no point on sending them any email, or even keeping the address.

All right, they could use a different computer or a different email account. But that'd be a bit weird.

But in any case the sensible thing with an address you aren't going to use, but don't want to lose, in case of some kind of emergency, is to write it down in a book, not rely on the computer with all its funny little ways of screwing things up.