Sender ID is an authentication protocol used to verify that the originating IP address is authorized to send email for the domain name declared in the visible “From” or “Sender” lines of the email message. Sender ID is used to prevent spoofing and to identify messages with visible domain names that have been forged.

The 3 Things To Avoid When Emailing Your List
When you decide to have an opt-in list, it is not just a matter of sending your subscribers your promotional newsletters or catalogs.