How does it determine a DSN (to avoid creating a DSN for another DSN)?
I don't have the source code, so I guess it uses the NULL sender. In
addition, it may use content type check, but I don't know if it does
that.
The standard method is a null return path -- But if IIS is sending mail
which isn't using a null return path, does it have some other method to
determine a DSN from a regular message?
IIS SMTP sends the DSN with NULL envelope sender/return path. If it
wouldn't do, the Internet would have already crashed, considering the
number of Exchange servers (which use IIS SMTP for SMTP transport)
around :)
The SMTP server of IIS is suprisingly standards-compliant. For
example, it generates DSN's according to RFC 1894, while Internet is
full of mail servers that does follow this RFC (from 1996). My ISP's
Exim server (4.44, from 2004) send me bounce reports that cannot be
easily machine-processed due to their non-standard format, so bounce
managers has to use VERP, which causes issues with Exim's and most
notably Postfix's sender callout verifications, greylisting, etc. Just
venting :)
Peter