▁the ▁clients ▁could ▁support ▁B cc : ▁functionality . ▁This ▁functionality ▁was ▁not ▁exposed ▁to ▁Microsoft ▁Mail ▁for ▁PC ▁Network s ▁users ▁due ▁to ▁limitations ▁in ▁the ▁server ▁architecture , ▁but ▁the ▁corpor ate ▁internal ▁M API . D LL ▁en abling ▁these ▁particular ▁clients ▁to ▁talk ▁to ▁X enix - based ▁mail ▁transport ▁systems ▁util ised ▁this ▁functionality . ▁The ▁first ▁and ▁almost ▁immediately ▁re called ▁version ▁of ▁the ▁Microsoft ▁Press ▁book ▁on ▁using ▁Microsoft ▁Mail ▁accident ally ▁used ▁screens h ots ▁from ▁the ▁X enix ▁backend , ▁reve aling ▁this ▁conce aled ▁cap ability ▁of ▁the ▁client . ▁ ▁Gate ways ▁ ▁Con ne ctions ▁to ▁other ▁email ▁systems ▁were ▁made ▁possible ▁by ▁gate ways ▁to ▁" fore ign ▁mail ▁systems ". ▁Microsoft ▁sh ipped ▁gate ways ▁to ▁PRO FS , ▁SN AD S ▁( Office ▁V ision ), ▁SM TP , ▁X . 4 0 0 ▁over ▁X . 2 5 , ▁Nov ell ' s ▁Message ▁Hand ling ▁System ▁( M HS ), ▁M CI ▁Mail , ▁AT & T ▁Mail , ▁and ▁others . ▁Many ▁companies ▁running ▁these ▁gate ways ▁quickly ▁replaced ▁them ▁with ▁Microsoft ▁Exchange ▁Server ▁connect ors ▁once ▁Microsoft ▁Exchange ▁ 4 . 0 ▁sh ipped . ▁In ▁particular ▁an ▁early ▁part ▁of ▁a ▁migration ▁from ▁MS Mail ▁to ▁Exchange ▁included ▁replacing ▁the ▁Microsoft ▁Mail ▁for ▁PC ▁Network s ▁Gate way ▁to ▁SM TP ▁to ▁the ▁Microsoft ▁Exchange ▁Internet ▁Mail ▁Con ne ctor , ▁later ▁renamed ▁to ▁the ▁Microsoft ▁Exchange ▁Internet ▁Mail ▁Service . ▁ ▁Connection