I have the SMTP service installed on Server 2008 R2. Under Domains, if I go to properties, under Route Domain, I have the option to forward all mail to smart host and I currently have one address [nnn.nnn.nnn.nnn].
Is it possible to have more than one address here? [nnn.nnn.nnn.nnn];[nnn.nnn.nnn.nnn] or [nnn.nnn.nnn.nnn],[nnn.nnn.nnn.nnn]?
Read the RFCs for SMTP. It will give you all the information you will need to know. If you need more functionality than this, you'll need an email server.