It seems to me that encrypting emails is either untenable or insufficient depending on how you do it. You could do a one-way operation like is used on passwords, but then you can't access the user's email address to send them emails. You could instead do a two-way encryption but that likely means using a hardcoded key to decrypt, and that key can't be considered secure if attackers have access to the system. There may be other more effective options but I'm no security expert and I haven't given much thought to other solutions.