You should only send emails from a valid email address.

You should only send emails from a valid email address. When sending to a mailing list this should be
from the domain / web site that the recipients originally signed up with so they will recognise the email is
from you – we would typically not allow sending from ‘free’ email addresses, your ISPs email address or
using anonymous email addresses unless your users specifically opted-in using that exact address. http://www.dailysender.com