I don't have email with my T, but I can email my nutritional T. The boundaries, however, are the same.

With my T I can call and leave a message, but T will not call back unless I specifically ask for a return call.
With my NT I can email any time, but again, NT will not return my email unless I specifically ask for it, and even then, it is only confirmation that the email was received.

All content from either call or email is discussed at my next appointment.

I know what you mean, though. I feel an incredible sense of relief after I either leave that voicemail or send that email. It's as if I'm sending my thoughts out there and they aren't stuck inside my head anymore.

I'll also say that any email or voicemail is carefully written out so it is as concise as possible, often I'll write two or three drafts in my journal first, to see if I really need to share it, and then if I do, I edit down one of the drafts to the shortest and most concise length as possible. It still helps me to get it out there, but I know I'm not dropping anything unnecessary.