Cannot find SMTP server

2 win xp boxes, dhcp, through a Linksys DSL router. Identical Nics (3Cr990TX). If I configure Outlook 2002 or OE 6 on both boxes with identical email accounts, one box can send mail, the other cannot. I am stumped – since I’m using DHCP served up from the Linksys box the IP stack on both boxes should be identical, the mail setting are identical (I’m using the same email account on both boxes for testing purposes).

Any ideas????