What authentication requirements exist for 2024-25 bulk sender rules (Gmail/Yahoo)?

In early 2024, Google and Yahoo established new maritime laws for any fleet sending over 5,000 messages per day. These rules are non-negotiable for reaching their harbors.

The core requirements are:

Full Authentication: Senders must have SPF, DKIM, and DMARC implemented for their sending domains. DMARC Policy: The DMARC policy (`p=`) must be set to at least `p=none`. A policy of `p=quarantine` or `p=reject` is strongly encouraged. Alignment: The visible `From:` domain must align with either* the SPF domain or the DKIM domain. One-Click Unsubscribe: Messages must include a one-click unsubscribe header (as defined in RFC 8058 and RFC 2369). Low Complaint Rate: Senders must keep spam complaint rates below 0.3% and are strongly advised to stay under the 0.1% threshold to avoid filtering. * Valid Infrastructure: Sending servers must have valid reverse DNS (rDNS) records, also known as PTR records.

These rules are the new standard for safe passage. Failure to comply results in messages being deferred or rejected outright.