Notes/Domino 4 and 5 Forum

Hi,
could somebody help me with my problem. Our LN administrator left and I was asked to find out how we can change MTA server name. Our mail goes through the external MTA server and now we need to replace it with the new one. I don't know where to change the server name from old name to new to re-direct mail to the new one. Is it only one document affected?
Thank you