Interesting idea for a thread. Though I have to say I read your post slightly differently. If you email a second time, you've broken the boundary. Your T is then responding to that. I don't mean to nitpick! I just think it's worth distinguishing between a) a boundary breach that is instigated by the client and b) a T being the one to break the boundary in the first place.

In the scenario you describe, I think it's confusing if the T just changes things without actually acknowledging that this has happened. I don't think scolding is the way to deal with this - do any Ts actually do this? I think it would be better to simply and clearly re-state the boundaries. I also think one email a week seems like a problematic boundary to start with, because what if something major happens just after you send the email?

I'm probably the wrong person to answer this as my T's boundaries are limited to the basic, immoveable ones where, if he breached them, I would have to leave therapy. He doesn't have rules about things like how many emails I can send, or whether he passes the tissues, or anything where breaking the boundary would be a trivial matter.

Personally, in that situation I would be more concerned about the purpose of the boundary. Why one email? At what point in the week are you supposed to know if you're ready to decide what to email about? Why are you limited to one email? Why can't your T allow you to email without committing to reading or replying? The whole idea of it makes my head ache a bit, so I imagine the client in that situation would feel the same.