As I said in my e-mails, you are going to need to put the address in a few places. If SMTP Authentication is on (which it most likely is):
Utility / Counter
Administrator Settings > 12345678 Password
Network Settings
E-mail Settings
SMTP
Detail Settings
SMTP Authentication ON
Enter the Username and Password here

Once you have done that, you will also need to enter it under:
Utility / Counter
Administrator Settings > 12345678 Password
Administrator / Machine Setting
Input Machine Address > Enter Name and Address Here
Administrator Address > Enter Name and Address Here

If you don't set the Machine/Administrator Address, when you try to send an e-mail, the start button may be orange, saying that no from address is set. Alternatively, if they have an address in there that is not correct, some servers will give you a login or forward TX error if the e-mails do not match.