Recently, a colleague at work was struggling with one of our new Windows 2008 servers, in that it wasn’t sending emails out to users. It turns out that there’s a historical reason for this, which I shall outline below:
IIS4/IIS5 were aimed at classic ASP, which used CDONTS to send emails. CDONTS wasn’t aware of external mail servers, it assumed you’d run a single-box environment, so is hardcoded to use localhost and the cutdown SMTP service bundled with IIS: http://classicasp.aspfaq.com/email/can-i-use-a-remote-smtp-server-with-cdonts-newmail.html
IIS6 and above use the replacement, CDOSYS, which is aware of remote servers, so you don’t necessarily need your web server to run a local SMTP service: http://www.asp101.com/articles/john/cdosmtprelay/default.asp
IIS can still run a local/cutdown SMTP server, and this can still be managed via IIS.
IIS7 seems to further this concept and do away with local/cutdown SMTP service under IIS altogether. Although SMTP server can be installed on Windows2008, it’s considered a separate product (and not manageable from IIS7, IIS6 is used with it’s compatibilty mode); Instead, IIS has the option to use an external SMTP server.
http://weblogs.asp.net/steveschofield/archive/2006/12/19/iis7-post-23-vista-and-smtp-server-where-is-it.aspx (Note: Vista runs same ‘core’ as Windows 2008)
