Did you have problems setting up PHP on a Windows server which is running IIS and also running an SMTP server inside IIS? Have you faced problems sending mail from PHP scripts running on IIS server with IIS SMTP engine? By default, IIS doesn’t allow relaying SMTP emails if it comes from 3rd party products. So this problem is related to IIS SMTP “Relay Restrictions”. Sometimes some of my clients are using PHP on windows servers using IIS 6 as the web server. In linux PHP supports native sendmail system from the OS itself. But in windows, you need to tweak your way to make PHP able to send out mail from localhost. If you are a .Net developer, you might already know that from ASP.Net codes or even Classic Asp code it’s just as simple as 1,2,3 to send out email or use the IIS local SMTP server. Let me make it simple for you so that you guys can make use of the localhost server from PHP.
There is more information at the end of the article about using XAMPP Sendmail in Windows.