Being honest and true to yourself first, is the best way of answering his email.
Secondly, I feel he has made a good deal of progress with saying he understands he is angry with himself, and not you, with also seeing his anger is really guilt. I think being positive about his statement, AND kind allowing him to get the idea he is working in the right direction... how you do this without sounding like a "parent" is going to be rough.
Let him know you appreciate him being so candid, and his heartfelt appology is accepted in hopes that one day it will lead to more positive co-parenting, as the lines of communication can be opened/widen with acknowledging our own issues and putting them aside, for the best interest of D.
I would try to keep things as uplifting as possible with the understanding things can go south in the next email... or possibly get even better.... it's a crap shoot on the rollercoaster, as you all ready know.
Good Luck W8ting.... blessings
Jeremiah 29:11 For I know the plans I have for you.........
