Once you install SMTP on IIS, Drop box will be created automatically.
Open IIS manager -> Default SMTP virtual Server -> Domains -> MOSSserver.domain.com -> Properties.
Check the drop directory location, default location would be "C:\inetpub\mailroot\Drop" where all the emails will be stored till Sharepoint timer service pick it up. Sharepoint timer service will check this folder every 5 minutes (default). The timer job that picks up mail runs about every 5 minutes or so, so you should not see the email sit there for long
"Microsoft SharePoint Foundation Incoming E-Mail" service will pick's up the emails from the drop folders and sends to the required location using the
X-Receiver headers in your emails, these headers is automatically added if you use the SMTP service in Windows.