I have a Windows Server 2008 R2 server with the SMTP service enabled, which provides mail relay to another server for some applications.
Sometimes, a message comes in with a wrong "To:" address, consisting of only a single word without a SMTP suffix, i.e.
someone instead of
When this happens, the server treats the message as being addressed to its own fake local domain, i.e.
email@example.com, and drops it into its "Drop" folder.
There is, of course, no user named
someone on the server, and that address is obviously invalid; and yet, the server still drops the message there, instead of sending a NDR because
someone without any domain suffix is not a valid SMTP address.
How can I force this server to send a NDR when such a message is received?