If a constituent has previously unsubscribed or opted-out of email, and then opts back in to email, they still won't get any communications unless they receive the "unblock me" email, which looks very much like spam. If they opt back in, that should be the only step needed. Otherwise, we have to search for who may have once opted out and opted back in, then send them a message through gmail explaining the situation and letting them know about a suspicious-looking email asking them to submit an "unblock me" request. It's time-consuming and damages our credibility with constituents.