Well, not anymore. Despite the error message I got, the system shows my "new" email address as the one it is using, and my "old" email address received a notification that the address had been changed.
Thanks @bbbales2 for the tip. That looks like what I wanted, at least for receiving posts via email. It looks as if one can respond to individual posts by replying to the email; I don't see anything about creating new topics via email.