SpamAssassin Rule: SPF_HELO_PASS
Standard description: SPF: HELO matches SPF record
SPF (Sender Policy Framework) is an open standard specifying a technical method to prevent sender address forgery. The domain in the HELO command is matched against a list of allowed mail relays for that domain. This states, for example, that mail from email@example.com should have come via mail.example.com and not mail.badguys.info.
In a normal mail client, the HELO command uses the internet name of the computer sending the mail, so that someone might use their computer 1-2-3-dyn.bigisp.com to send mail through bigisp.com's mail relay, which has an SPF record indicating that that's allowed.
A "Pass" result means that the client is authorized to inject mail with the given identity. The domain can now, in the sense of reputation, be considered responsible for sending the message. Further policy checks can now proceed with confidence in the legitimate use of the identity.
From RFC 4408
The default scores for this rule can be found in the online list of tests.