====== Setting SPF and DMARC for a domain that is not sending e-mail ======

Set the SPF TXT record (domain.com) to:

<code>
v=spf1 -all
</code>

This will inform receiving mail servers that no servers are authorized to send mail from this domain.

Set the DMARC TXT record (_dmarc.domain.com) to:

<code>
v=DMARC1; p=reject;
</code>

This will instruct receiving mail servers to reject mail that if it is unsigned or when signature verification fails.