Husband and his Ex Wife

My husband has a 4 year old with his ex wife. I understand there has to be a level of communication, for his daughter. He HATED his ex for the first year they were divorced, like he was a straight up ASSHOLE to her. But now it's all buddy buddy and friendship like thing.

Is it wrong of me to be upset that they talk nearly everyday, even when it's not about his daughter? Maybe I'm just hormonal but it REALLY gets under my skin.

He sought out comfort from her when he found out that he was going to have to leave the military due to higher tenure. And he talks to her about random things all day. I don't even have small talk with him throughout his work day...

On top if it all, it's always on his work email, I don't go through his messages like that, I mean we share all of our passwords with each other but his work email is only accessible with his military ID card and while he's on base. Is that not weird? Now when he deployed August 2014, 6 months after we got married, I found emails between him and her that were "talking about old times and her feelings for him". To me that's inappropriate... so of course I'm still uncomfortable about it even though we talked about it.

So am I hormonal or would you feel as crazy as I do. I don't know what to do. I tell him it bothers me and he just shrugs it off...