How to resolve Spoofing errors for everybody at your domain name
Traditionally, email discussion groups leave the sender's email address in the From header of the email.
So a message to the mailing list comes from the person that sent it, even though the Mail-List.com servers are delivering the email.
This confuses some ISP's and they will block the incoming email as being spam, since they are not expecting email to be coming from any place but themselves.
Example of error messages that you might see
550-5.7.1 Your message has been rejected. The host which delivered your email is not listed as an authorized for the sending domain.