configuring emails at our branch offices

we have a domain name and mail id’s as name@companyname.conm, and our main office had m- deamon as a email collection a distribution S/W.
We have a dedicatee ADSL line at our main office.
I need give email ids to our staffs at the branch offices in the same manner ( they donot have any dedicated line.),. How do i go about to use email ids as name@compnayname.com. Do i have to install m-deamon at our branch offices too?..Is there any way i could have their names configured in my Main offcieand have these mails sent from my main office,,,,is there a possiblity of such a dialing to my server an NT machine possible? Can any one help me with a solution?
thanks in anticipation