It's clear to everyone (I hope) that storing passwords without at least salting/hashing them is a terrible idea.
What about emails? Let's say you keep the subscription email address, if you encrypt it properly it may not be usable to send emails to the users. On the other hand, if you don't encrypt it and the database gets stolen, all your users risk a potential spam.
This question is not about law-specific issues (although they may be given, they remain country-dependent) or about encrypting the database itself.