[epub] Clarification please, John Glube

["Wonder Wyant" <wonder@xxxxxxxxxxxxxxxxxxxx>]

* Publish an SPF policy record for your domain, as the
larger ISPs like AOL are using SPF record checking to
verify the email source for bulk mail. To avoid problems
with message forwarding, end the record with ~ all.

I'm sorry but I don't really know what this SPF policy record is.  Could 
someone please enlighten me?

Thanks,
Wonder