SMTP Problems

I'm trying to send an email woth the mail function on PHP... I configured in the C:\winnt\php3.ini these lines (this is on a Windows Machine [Win32]) SMTP = smtp.domain.com sendmail_from = user@domain.com And when I run my script my page times out. The SMTP server is a Linux Box. I configured sendmail to allow relaying from the NT machine (running PHP) and I tried with an email client (MS Outlook Express) with the same setting (SMTP Server and user) and it works fine!! I also telented to port 25 from the NT machine and could manually do a SMTP session. Can anyone help? Thanks Sergio