As a faithful 12-stepper, I believe everything happens for a reason. So I would say discovering the email account and being able to access it was a gift. In my case, AH left his password on my computer one night while he was (drunk) checking his emails.
I say this, of course, because I did the same LOL. Not only emails, but journals. For 18 years AH kept journals and not once did I ever look in them. When he came to get some of his stuff from the house, he left the journals behind. Still don't know if it was subconscious on his part or not, but I began to read them. Mostly I went to the dates where I had doubted my sanity on his behaviors. There is one page from those journals that I still carry in my therapy notebook. It illustrates the absolute insanity, fear, self loathing and everything else I've heard about from attending open AA meetings. All of it isn't important to share here, but in one page he starts with expressing his absolute terror at the thought of losing me, and ends with his fear that his resentment and rage against me is so strong, he will kill me in a blackout.
I changed the locks and installed a security system. I consider those journals being left behind a god shot and I have no regret at reading some of it. i haven't looked at them since and don't really have an interest.
I can't imagine ever doing something like that again, because I hope I'm learning enough to know to leave an unhealthy relationship before it gets to the point of having to check emails and journals.