In test and development, sometimes you don’t want to send the mail, you just want to write it to disk for reading as an .eml file.
IIS’s SMTP writes email to C:\Inetpub\mailroot\Pickup
To let ASP.NET use that, first, you can’t do it in medium trust. You can only send email over port 25 in medium trust, not to the drop folder.
YOu will also need this link: http://agileer.com/blog/2007/05/24/CannotGetIISPickupDirectory.aspx
Editing the metabase may be required.