With the same php3.ini file I can send email using the mail() function using php-3.0.11.  After that version, all of them (till 3.0.16) generate an Illegal operation error.

I have tried to setup the SMTP directive, using IP numbers, or names, put some equivalent names on the HOSTS file. It doesn't work.

Test script is:
<?php
echo sendmail("sromero@usa.net", "Test mail", "This is a test mail");
?>

I'm using the pre-compiled version of php for win32, downloaded from the php site.

The only changes on php3.ini file are on the SMTP directive and the sendmail_from directive, to reflect the SMTP server and address accordingly.

The operating system is Win98SE and WinNT4 SvcPack6, the SMTP server it's an Exchange SMTP server on WinNT.  Tried to run the script on both machines.