Hi cienfu,
I was going to ask you to explain a little better and I don't really know much on the subject, but performing a Google search I found some results that may interest you:
h**p://androidforums.com/threads/using-exchange-email-and-mandatory-pin-lock.673164/
h**p://forums.androidcentral.com/google-nexus-4/264479-disable-pin-lock-exchange-policy.html
Please see if this is your case.
I also found email apps that circunvente this safety feature, but disencourage you to do so.
Hope it helps.