The main thing, in my opinion, is whether between the two of you, you can work out a consistent system that will work for both of you.

Stuff happens during the week that may trigger us or stress us out, even if it's just thoughts we're having. When humans are stressed or triggered, our attachment system fires up, whether we are aware of that or not. What happens next determines the outcome.

Basically, the question is, do we respond to the distress and the activation of the attachment system in a way that regulates the distress or in a way that makes it worse?

If you can reach out to someone when distressed, whether that is your T, another person in your life, or an internalized version of a positive attachment figure (like picturing getting a hug from someone in your mind), and the contact whether real or imagined soothes your distress, then that is the ideal situation.

Sometimes reaching out to someone when distressed is so fraught for people with trauma histories that they have to learn other ways of handling distress first. That's where self-soothing skills come in. Even though part of you may want to reach out to your T or someone else, another part of you may be terrified to do that. So instead, maybe you listen to a guided meditation or go for a walk or whatever you have learned to do that can settle your nervous system. It's not ideal (in that this type of self-regulation will probably never be as effective as being able to rely on an attachment figure) but it still solves the problem in the moment.

In the worst case scenario, maybe you want to reach out but then you're afraid you're not supposed to. Now you have an internal conflict which is increasing your distress even more. Or maybe you do reach out but don't get a response or get a different response than what you wanted. Now maybe you feel abandoned on top of distressed, or you may feel shame and anger. So your distress again is amplified instead of settled.

Basically you should have a system between you and your T that when you are distressed, you can settle it consistently (if not 100% of the time, at least a majority of the time) without making it worse. If email can work for that, great. If phone calls work, great. If having someone besides your T to contact works, great. If self-soothing strategies work for you, great. If having a recorded message from your T works, awesome. I have used combinations of all of those things at different points in my own therapy. They worked most of the time because it felt like a collaboration and because T was fairly consistent with how she responded to emails and phone calls. If they know they can't be consistent with one method, it may be best to rely on a different one.