Today ISP’s are seriously working to rid their networks of spam. Email authentication can
help these ISP’s to validate that the email is originating from a legitimate
source and the recipient can validate the mail source. All major ISP’s
like Hotmail, Gmail , AOL, Yahoo! and use email authentication to filter out
suspected spam emails.
By setting up Email Authentication, you can enable these ISP’s to verify
that your campaign are from a “legitimate” source, and being delivered
to your target’s inbox, instead of being flagged as spam.
For example, here's an authenticated and non-authenticated email in Hotmail:
