[Gemme]

I hear what some are saying about not responding at all and, no, you don't have an obligation to respond to the email but it feels shitty to me to not at least acknowledge it. That doesn't mean acquiescing to it but we are human creatures and it's hurtful when someone reaches out, for whatever reason, to be rejected or ignored.

Having said that, there was a time when someone sent me an email and I. Just. Didn't. Know. What. To. Do. With. It.

Awkward and frustrating times 1000.

I was at a complete loss so I didn't do anything.

And I feel shitty about it but it's too late now.

Sooooo.....that's my looking glass that I'm seeing this through.

I think Sleepy and QueenofSmirks' advise was closest to what I might do. Acknowledge the effort, because it does take effort and most people would not take it lightly opening up old wounds. But no, you don't have to forgive. I'm not a forgiving person and I do hold grudges myself and I don't think that that has stunted my personal growth or harmed me. You have to be true to yourself.

How about this?

"I appreciate your apology. I'm glad you are taking steps to get happier and healthier and wish you good luck in your journey."

That is, assuming you are glad they are not as douchy as they once were and that you do wish them well.

If not, then a simple, "I appreciate your apology. Good luck." might work too.