I'm not sure about "mandating transparency." I have an urge to say, absolutely no, don't mandate. Just step back and trust that she will conduct her life in the best interest of herself, you, and the kids. If she is hellbent on straying or seeking something outside the marriage, there is probably nothing you can do from stopping that (mutual transparency or not.) But, I think I've read posts on alternate viewpoints on this with someone who has recently cheated... Perhaps others will comment on that.
I mandated the transparency, and she reluctantly gave it. Now she is saying "I hate that you are reading my private mails with my friends" "I want my privacy" "I hate that you are spying on me - it's controlling and ugly". She is now watching me trying to catch me spying on her. She is planting things in her mails to make me mad so that she can prove her point. (so far I haven't gotten mad because I haven't read her mails, and therefore did not fall for the trap).
She won't change her passwords now on her own, she'll just resent me for not wanting her to.
At the same time, she will still email OM if she wants to - she would just delete the mails from her inbox and outbox immediately to destroy the evidence. So since the transparency is not willingly and openly given, I am not sure if it is buying me anything. It is not really helping me to trust her, and it is definitely hurting her ability to trust me.
So I am considering making a trust-building gesture, and telling her to change her passwords.
2 months ago, I would have said "No F'ing Way", but now I am a bit more detached. I don't want to hold onto transparency as a false security blanket if it is actually harming my sitch.
Me 42, W 39, S8, S6, S2 M 11y, A & ILYBNILWY 11/08 Walking away from a bad situation.