1. The easiest thing to try would be to telnet to port 25 on the mail server from the desktop where the script fails. This wil check your connectivity with the mail server. Microsoft has a knowledge base article with the details.

2. You might want to check if the mail server logs show any errors that contain the IP of the workstation where the script fails.

3. You could try downloading a protocol analyzer that will run on your Windows desktop, such as Wireshark . This will show you the whole conversation between the script and the mail server, including error messages that might be returned by the mail server. If the problem isn't obvious, do the same thing on the desktop where the script works and compare the results.

P.S. The commands in the Microsoft article are valid for Sendmail and other open source mail servers as well as for the Microsoft mail server line.