Dear T,

Thanks for updating me that you hadn't had time to really focus on my e-mail and would respond thoroughly tomorrow morning. I had started to worry it had annoyed you, and your update made me feel better... MC would have just let it go for a couple days, which would have led to me sending follow-up e-mails/texts, which was probably really annoying. But just an "I got your e-mail, will respond when I can" means a lot... Because it shows you're (presumably!) not annoyed and that you haven't just ignored me...
--LT