Dear husband,
I really understand how you feel, unsecured and hurt. I must commend you as a loving husband and that your wife is a straight forward person for not denying the fact that she actually wrote the words of her mail but rather seek your forgiveness, to the extent of begging you to punish her if you still feel that what she did is really wrong so as not to ruin your long coming pretty relationship. And i want to say for her to have kept the mail undeleted knowing fully that you have access to her mails should be able to convince u she has probably done nothing bad behind you.
I will advice you forgive your wife and move on as there are so many men out there who need a woman of these qualities and might want to advise you send her away because they are not as lucky as you are. God bles you as you make your wise decision.
Regards.