Dear T,
Are you still reading my emails? I know you missed one while I was on vacation which I completely understand. I miss emails all the time, although I’d be less likely to miss an important one. I can’t help but think that if I was interesting to you, you wouldn’t have missed it. Just want to make sure you’re not sending a subtle message. We’ve had this email arrangement for a long time, so maybe you’ve decided it’s time to change things. It’s happened before, so I just wanted to check.