This is just a hypothetical consideration: some (or many, very many, i think) would find very useful an on / off switch for the internal mail system. 

In "on" mode, all mail system remain as currently.

in "off" mode, the player still continues to receive both the automatically generated communications by "Mr.Black", both communications from their combine mates (if adhered to a combine). Also the mails from six partners in join ops centers and from "add to friends contacts" remain allowed. (pass through concept). 

All other communications, from extraneous players, would like to automatically rejected.

Personally i really appreciate this hypothesis, so i bring this to the attention of The Syndicate's engineers.