The library necessary for CDONTS functioning is no longer provided with windows 2003 / IIS.
You have to use the CDO component to send a mail.
Here is an example of a script used in replacement of the CDONTS script:
<%
Set objErrMail= Server.CreateObject("CDO.Message")
With objErrMail
.From = "From Address<from@domain.com>"
.To = "recipient@domain.com"
.Subject = "Subject Line"
.HTMLBody = CStr("" & strBody)
.Configuration.Fields.Item ("http://schemas.microsoft.com/cdo/configuration/sendusing") = 2
.Configuration.Fields.Item("http://schemas.microsoft.com/cdo/configuration/ smtpserver") = "IP of smtp server"
.Configuration.Fields.Item("http://schemas.microsoft.com/cdo/configuration/ smtpserverport") = 25
.Configuration.Fields.Update
.Send
End With
%>