Not that this has anything at all to do with DW, but this is
very a common trick by spammers to get their garbage past spam
filters, since most are set to let the user pass through
I receive mail from "myself" at home, and at work with a work
email address
I also receive bounced mail where my address has been used as
the return by the spammer
There is nothing you can do to stop this type of spam... but
you can preview and delete before downloading to your computer from
your server (for many types of servers anyway) by installing a
product such as Mailwasher
http://www.firetrust.com/