This is an ISA configuration issue. You need to make sure that ISA is configured to allow port 25 (SMTP) from the internal network (Small Business Server included) to the Internet. ISA can be tricky to configure, and when it is integrated on the same server as the applications it is trying to protect, you are talking even more complexity. I would suggest, as a best practice, you use a separate server to set up ISA or simply use an inexpensive firewall device instead. I think you will have better luck.
MEMBER FEEDBACK TO THIS ASK THE EXPERT Q&A:
With Windows Small Business Server (SBS) 2000/2003, you also need to be a member of the BackOffice Internet Users security group or ISA Server won't let you browse the Internet or send email out. If the other systems are not having problems with email or browsing, only the laptop, then ISA Server is not going to be blocking port 25 outbound.
Do you have comments on this Ask the Expert Q&A? Let us know.
Related information from SearchExchange.com:
Dig Deeper on Exchange Server setup and troubleshooting
Related Q&A from Richard Luckett
Some folders in a mailbox on Exchange Server 2013 are not showing up on the folder list in the OWA virtual directory but do appear in other views. Continue Reading
We have a Client Access Server and Mailbox Server on Exchange 2013 and we want to install an Edge Transport role on another machine. I joined the ... Continue Reading
How can I enable Outlook Anywhere to allow internal use for all users and external use for only some users in Exchange 2013? Continue Reading