Setting up SPF record for a domain that never sends email

[itsme2003]

I provide computer support for a company that uses two email domains, lets call them DomainA.com and DomainB.com.

DomainA.com is used to send and receive email in a normal fashion. DomainB.com is used only to receive email. If someone at the company replies to an email that was sent to the DomainB.com, the reply is sent out from the mail.DomainA.com server. In other words no email sent by this company will ever be sent from mail.DomainB.com and the senders address will always be user[at]DomainA.com.

I'd like to set up an SPF record for DomainB.com (the SPF for DomainA.com is already set up) that reflects the fact that there are no legitimate senders of email for DomainB.com. That way anyone who is checking SPF records will correctly determine that the email is not legitimate.

One way to do this would be to simply set up a bogus address as the authorized sender (sorrry, but I don't know the offical terminology of SPF). I could use a bogus (for me) address such as 1.1.1.1 or something in the private ip range such as 192.168.0.1. That way any message claiming to be from DomainB.com would be revealed to be bogus when checked against the SPF record, since whatever address it was sent from would not match the address that I had entered into the SPF record.

Is that the best way to set this up, or is there another way to setup SPF for a domain that never sends email.

Thanks in advance for any assistance.