Email Program Will Not Accept Address

Every time I go to set someone up with a live mail account and use their in existing email address the wretched program will not accept the address they already have and keeps requesting that it has to be set up as a hotmail one. If I ask it to use their own address it comes with some rubbish aboout being in anaothe domain or something. Am absolutely sick of this program why in the name of reason cannot the damn thing just accept the persons existing address. I mean no one wants to start letting everyone else a new address to send to them especially if they have a lot of contacts. I set my own up so what is the go with it now and this one and only feature makes cleaning up someones machine a nightmare.