Do the rules apply to small senders?

The strictest rules target senders of 5,000+ messages a day to Gmail, but authentication is expected from everyone.

What about one-click unsubscribe?

Required for bulk marketing mail; it is set in message headers, which a DNS check cannot see.

Google/Yahoo Compliance

Gmail and Yahoo require bulk senders to authenticate with SPF and DKIM, publish DMARC, align the From domain, and have valid reverse DNS and TLS. This check grades a domain against each of those requirements and shows which ones fail.

When to use this: Gmail or Yahoo is rejecting or junking your mail, or you send more than a few thousand messages a day. Command prefix compliance-google:

About the Google/Yahoo Compliance

Grade a domain against the Gmail and Yahoo bulk-sender requirements: SPF and DKIM, a DMARC record, aligned From:, reverse DNS and TLS.

FAQ

Do the rules apply to small senders?: The strictest rules target senders of 5,000+ messages a day to Gmail, but authentication is expected from everyone.
What about one-click unsubscribe?: Required for bulk marketing mail; it is set in message headers, which a DNS check cannot see.