Dear Kerry,
I can most certainly understand your concern but only because I once would have been as concerned as you are and upset as you are if my husband was doing this. I'm 54 years old and have been around the block more than a few times. I am in a very happy and successful marital relationship going on 32 years. I've been married before and so has he.
Here is what I've learned over the years and perhaps it will help assuage your fears.
First of all NO e-mailing is NOT a form of adultery at least not in the way you've described how your husband is doing it.
Second of all and perhaps the MOST important thing is do not and I mean DO NOT ask your husband to stop. Don't ask him to change for you and most especially don't ask him to stop having close friends of the opposite sex. If you insist on it I can guarantee you that your relationship with him will suffer immensely. If there is one thing I've learned in 30 years of marriage (and yes I've had other intimate relationships so I have some experience in this area) is that we can't restrict our partners from being who they are and from having friendships with who they choose. If who they are and the friendships they choose is so hurtful to us and is truly harming us in any way then it's our responsibility to end the relationship but it's not our right to try to force them to change. We are who we are and we should all be allowed to be who we are and to have friendships with who we want to have a friendship with.
You have to take a minute here and be completely and totally honest with your self. From what I read ALL of this is about 'you'. It is your fear of what might happen or what's already happened that you don't know about that is the main issue here. I don't see where your husband is doing anything wrong except being the sort of person who can maintain a close friendship with a person of the opposite sex WITHOUT sex being involved. That is a very rare thing and something that you should treasure in your spouse, not something you should fear. It is the spouse who CAN'T have close friendships with those of the opposite sex that you need to be suspicious about...those are the ones who will say it's only a friendship and it will turn out to be something else (been there and done that).
I have very close lifelong personal friends who are male in my life. My husband has always had close personal friends who are female. There is no jealousy and no reason for it. My husband, like yours, is completely open about who he is talking to or e-mailing and even who he is having lunch with or hanging out with. I am also completely open about the same for myself. Most of his female friends are from work and I don't really know them very well but I'm never suspicious of them. Why? Because I know my husband and I know that he is 100% dedicated to our relationship 100% of the time. He isn't jealous of my male friends because he knows the same of me. I 'trust' him but not because of what he hasn't done; it's because I choose to trust him until he gives me a really good reason not to. I don't see yet a really good reason for you not to trust your husband according to what you wrote.
It is possible for ex-spouses to remain close personal friends and still have wonderful relationships with their new spouse. I've seen it far too many times not to know it's possible. We can't be EVERYTHING ALL THE TIME to our spouses or to anyone else for that matter and when we accept that and become okay with it we are blessing our relationships with more joy that we ever thought possible. Your husband isn't being disrespectful toward you but you are being disrespectful toward him by assuming that it's perfectly okay to tell another human being, an adult, who they can and can't be friends with just because you are married to him. If you truly believe this is how a marriage works then you'll learn soon enough that a marriage like this can't work and yours will end. Why do you think divorce runs rampant in our society today? It's because of the 'idea' so many people have of what a marital relationship is 'supposed' to be. It's not an ownership...no one owns anyone else and no one has the right to tell another who they can be friends with I don't care what the marriage vows say. Those vows are old, outdated and come from a time when women were property and men did whatever men wanted to do. Things are different now and those old ways of being in a marriage no longer apply today. The ONLY way a marriage will work and both parties will be happy is if both parties accept the other for who they are, even the stuff they may not like so much, and doesn't ask the other person to change for them.
There will be those who will tell you to be very afraid and to make your husband stop this. It is the insecure person who will put the responsibility on their spouse for how they feel about things. They are fearful and insecure so they require their spouse to behave in a way so they won't feel fearful or insecure (typically when the spouse complies the insecure person will find something else to be fearful of and will ask their spouse to change yet again-no relationship can work this way). This is highly unfair to the spouse and isn't doing the person asking their spouse to be someone who they aren't any good either. At some point in our adult life we must accept responsibility for our feelings and stop putting that responsibility on others. No one can hurt us unless we decide to be hurt. No one can make us mad unless we decide to be mad. We decide how to see things and how to feel about them...no one decides for us. Those who can't accept this responsibility for their feelings and their reactions don't tend to do very well in life and tend, in my observation, to have many unsuccessful short-lived and usually very unhappy dysfunctional relationships. We can't hold others responsible for how we choose to perceive things. Again I only share this because I've lived it and learned to change how I see things and it has changed my life in such wonderful ways it's beyond description. I have been there and done that and learned better.
I can't stress enough how much we can't change other people so if we want something, like a relationship, to change then we must change our selves. If we can't do that or if we do and nothing changes then perhaps the relationship wasn't meant to be in the first place.
It sounds like except for this you have a pretty good relationship with your husband. DON'T throw it away because of your own insecurities because what you describe is a great foundation to build a wonderful loving mutually beneficial and satisfying relationship on that will last for many, many years..probably for the rest of your lives. I only say this because I've been where you are now, I changed how I looked at things, and everything changed. We have to truly look more at the wonderful things than at the things we don't care for so much otherwise the relationship is doomed. It wasn't five years ago I'd made up my mind to end my marriage. I wasn't happy and spent all of my time focusing on the things he didn't do for me that I wanted/needed as well as all the things he did that I didn't like so much. We have to learn to overlook the small things. We expect others to overlook those little quirks we have that others may not like...it's only right to do the same for others.
Five years ago in my mind my marriage was over after years of fighting to get what I thought I needed from my husband and to stop him from doing those things I didn't agree with. Then I decided to stop seeing him in that way and to begin to focus only on what he 'did' do and on the good things in our relationship. It saved our marriage. Nothing really changed except me but EVERYTHING changed and today I wouldn't have any other man in my life for anything. It is the blessings in our lives we must look at if we expect to get more of them.
Again if your husband can have healthy friendships with other women and be as open about them with you as he has been more power to him. That is something you should appreciate about him and value him for not be fearful of. If he can maintain healthy friendships with other women, be respectful of them and value who they are as human beings then you've got a man well worth holding onto because there are plenty of men out there who can't even see another woman without thinking of that other woman in a sexual way and then spend all of their time figuring out how to make that fantasy a reality. You are one of the lucky ones if you ask me. Here's how I see it. If my husband can be a good friend to other women besides me then it means he knows how to be a good friend to me and let me tell you from almost 40 years experience with being in relationships with men being friends is maybe one of the most important parts of an intimate relationship. There will be times when the 'love' wanes and that's when being friends will keep it together. This is personal experience and personal success speaking.
Good luck to you and remember...don't hold your husband responsible for your fears and insecurities. Being jealous never kept anyone from cheating!!!
P.S. After reading the other responses here I'm not surprised at them. This is how so many view a personal relationship...make him do what YOU want him to so YOU don't feel upset with him. How sad for them, really. Again this is why so many marriages fail in this country today. People, especially women it seems, want to hold everyone else responsible for how they feel and whether or not they feel safe in a relationship. NOTHING in life works this way; at least it's not functional or satisfying working this way. You are making a problem where it appears to me there is none. The bigger you make the problem in your mind the bigger problem it becomes between you and your husband. It's not your husbands responsibility to make sure you aren't jealous. How would you feel if you had a similar e-mail relationship with someone you knew like your ex or with someone you met on the internet? How would you feel if you knew you weren't doing anything wrong but your husband suspected you were cheating on him in your heart, even if not with your body, and demanded that you stop being friends with these people? You wouldn't like it I can promise you. In fact you'd resent it; you wouldn't like that he doesn't trust you even though you haven't done anything to betray his trust. We have to have the same consideration for other human beings, even our husbands, as we expect them to have for us. In sharing with you what he is doing and in allowing you to see what has been written by him and others it is painfully obvious to me that he feels he isn't doing anything to be ashamed of or that threatens your relationship with him. But you are making it a threat by your insecurity about it. You are the threat. Trust me...the more you accuse him of doing something improper the more you may drive him to actually do what you think he's doing. If someone continues to accuse you of something you aren't doing sometimes we think the only recourse is to do what we are being accused of OR end the relationship.
You can take the advice of whoever you wish, I have nothing invested in giving my advice, but I can promise you if you make this molehill into a mountain you'll be looking for husband number three in no time at all.