Tags: Sender-ID, SPF, DKIM, DK
DKIM / DK:
This only applies if using a combination of Postfix and Amavisd-new.
http://www.ijs.si/software/amavisd/amavisd-new-docs.html#dkim
Sender-ID / SPF:
http://www.openspf.org/
http://www.microsoft.com/mscorp/safety/content/technologies/senderid/wizard/default.aspx
http://www.microsoft.com/senderid