Hi, I'd like to help you with your question.
It sounds like you suspect your wife of at least having an emotional affair. You have found some evidence which makes it a possibility. Oftentimes, a husband or wife will have an off feeling that something is going on. It could be insecurity or it could be they are right. Since you have found evidence that your wife is communicating with another man and you have seen this email with the wet T-shirt, then you have enough evidence to suspect something is going on.
It may be that your wife has been truthful about not having a sexual relationship with anyone, but affairs can also be emotional. Being a confidant, sharing personal information that only a spouse should know, or encouraging inappropriate closeness are all cheating behaviors. By being emotionally open, there is also the risk of a sexual relationship.
Your wife should be open and honest about her situation. But it sounds like she is trying to make excuses. The most glaring evidence of this is her response to the wet T-shirt email. Honesty and openness is important if a marriage is going to be strong and last. Trust is the foundation and if you find that you cannot trust your wife because of suspicious behavior, then the marriage is in trouble.
The best option at this point is to confront your wife and let her know you are aware that she is not being faithful. Insist that the behavior stops and that the two of you see a counselor. If she refuses, go on your own. You need to find a way to cope with her behavior and determine if you want to stay in your marriage.
To find a therapist, ask your doctor for a referral. Or you can talk to your pastor, if you attend church. You can also search on line at http://therapists.psychologytoday.com/rms/.
Here are some resources that can help you:
The Emotional Affair: How to Recognize Emotional Infidelity and What to Do about It by Ronald T. Potter-Efron and Patricia S. Potter-Efron
Getting Past the Affair: A Program to Help You Cope, Heal, and Move On -- Together or Apart by Douglas K. Snyder PhD, Donald H. Baucom PhD and Kristina Coop Gordon PhD
You can find these books on Amazon.com or your local library may have them for you.
The most important part of recovering your marriage is that your wife recognizes that she has a problem and works on helping you trust her again. Your marriage can survive this and actually become better.
I hope this has helped you,