Well, everyone's email adress does not have to be totally public: The host could just send round a list to us of nations, forum nicks, and email adresses. As for realism, I tend to roleplay my diplo exchanges unless I specifically state that my remarks will be out of character.
I meant that the lag between diplomatic exchanges is somewhat realistic for a "medieval-esque" game. In the sense that diplomats have to go back and forth while fighting may be occurring; thus what is being discussed may not reflect the reality of the front.