That could easily be hyperbole on the author's part but you don't need internet if Red Hook residents are running their own mail servers. Since they could also possibly be running their own VOIP servers it isn't terribly far fetched.
Multiple non-internet based servers can easily talk to each other as long as they have a map of how to do so. RHI could be running their own DNS in which case each set of sendmail / qmail / whatever servers could still see each other. And if they really want to go old-school they could use UUCP or NNTP to shift around e-mail and news respectively between sometimes connected nodes. Many of the "intermittent internet connection" problems have been solved for a while.
Multiple non-internet based servers can easily talk to each other as long as they have a map of how to do so. RHI could be running their own DNS in which case each set of sendmail / qmail / whatever servers could still see each other. And if they really want to go old-school they could use UUCP or NNTP to shift around e-mail and news respectively between sometimes connected nodes. Many of the "intermittent internet connection" problems have been solved for a while.