When I first stated seeing my I, his boundaries were very similar - contact for scheduling/billing only. When I would email him (on rare occasion) for something like the even you are describing, I would always state that I knew what the boundaries were. For example, I might say...."I know your boundary for email is only billing and scheduling, and it's not my intent to push boundaries here, but I did want to send a quick note and follow up on (insert event here and give a very short outcome)." Also, I always clearly state that I do not need a response. Good luck!