Email for example.com

Who receives mail for this domain, who may send as it, and what happens to forgeries.

Receiving Nobody

Who accepts mail for this domain?

No MX record, so mail sent to this domain is not delivered anywhere.

Sending Anyone

Who is allowed to send as this domain?

No SPF record. Nothing states who may send as this domain.

Signing Nothing

What proves a message really came from here?

No DKIM record, so nothing signs mail from this domain.

Enforcing Nothing

What happens to mail that fails these checks?

No DMARC record. Anyone can send mail claiming to be this domain and receivers have no instruction to refuse it.

Edit

Senders (SPF)

Allowed senders

Usually include: plus a mail service that sends for you. Each one costs a DNS lookup. Receivers ignore SPF past 10 lookups. This record uses 0 of 10.

All other senders

Reject it Anyone not listed above is refused. DMARC needs this to work. Mark it as suspicious A soft failure: receivers usually accept it and flag it. Useful while you are still finding senders. Say nothing Says nothing about unlisted senders, so forgeries get through. Allow it Every sender passes. This is the same as publishing no SPF at all.

Saving rewrites the SPF record. HQ applies it within a minute.