I have installed IIS SMTP, but it does not appear in IIS Manager?

This is a known issue with IIS 5.0 and 6.0.

After the installation of the SMTP service on Windows Server 2000/2003, the SMTP tree may not appear in the IIS Manager console.
Click the "Start" button, then "Run…" and type:

regsvr32 %systemroot%system32inetsrvsmtpsnap.dll

Alternatively, %systemroot% can be replaced with the drive Windows Server 2003 is installed on (i.e. C:\Windows\ )