I think a lot of therapists sometimes do set clients up for unnecessary pain when it comes to emails and texting. Rather than being upfront about what they can and can't offer as an additional service, these therapists use vague language and are even condescending about how the limits will be set (allowing or not allowing email, for instance). Boundaries are usually set naturally, regardless of the relationship. If a therapist offers their email to clients, they should explain when they're available and what they can do. If I asked my T if I could email them, I'd want more of an answer than they'd worry about boundaries. To me, that says that he doesn't really know the answer.