Gmail sender requirements, plus Yahoo and Outlook.com rules

Changelog: what changed and when

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The latest changes at Gmail, Yahoo, Microsoft and Apple, month by month, are in our deliverability news.

Gmail sender requirements at a glance

Google’s email sender guidelines split the rules into two levels. Bulk senders have to meet everything in the “All senders” column too.

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Details that trip people up:

• The PTR record has to match. Google: the sending IP “must have a corresponding PTR record that resolves to a hostname”, and that hostname must resolve back to the same IP.

• 0.3% is the limit, not the goal. Google recommends keeping the spam rate “below 0.10%” and never reaching 0.30%.

• One-click unsubscribe means two headers (RFC 8058):

  List-Unsubscribe: <https://example.com/unsubscribe/opaque-token>
  List-Unsubscribe-Post: List-Unsubscribe=One-Click
  

• The headers don’t replace the link. Marketing messages also need a clearly visible unsubscribe link in the body.

To set up the records, see SPF record, DKIM record and what is a DMARC record, or create a DMARC record with the DMARC record generator.

Who counts as a Gmail bulk sender

Google’s sender guidelines FAQ defines a bulk sender as one that “sends close to 5,000 messages or more to personal Gmail accounts within a 24-hour period”. Three details matter:

• Messages from the same primary domain count together, so news.example.com and mail.example.com add up.
• “Senders who meet the above criteria at least once are permanently considered bulk senders.”
• The guidelines “don’t apply to messages sent to Google Workspace accounts”. Only personal Gmail recipients count.

Gmail bulk sender requirements: enforcement from 2024 to 2026

The requirements haven’t changed since February 2024; enforcement has. Google’s FAQ says that “starting November 2025, Gmail is ramping up its enforcement on non-compliant traffic”, and that non-compliant messages “will experience disruptions, including temporary and permanent rejections.”

What that looks like in practice:

• Authentication failures: messages “might be marked as spam or rejected with a 5.7.26 error” (what 550 5.7.26 means).
• Temporary failures: Google sends 4.7.x codes for authentication, TLS and PTR problems, which your server retries (421 explained).
• Permanent rejections: Google’s FAQ lists 5.7.x codes for the same problems: 5.7.25 (no PTR record), 5.7.27 (SPF failed), 5.7.29 (no TLS) and 5.7.30 (DKIM failed). Its SMTP error reference adds 5.7.32 (From domain not aligned with SPF or DKIM) and 5.7.40 (no DMARC record).
• Unsubscribe problems: Gmail doesn’t automatically reject these messages or send them to spam, but bulk senders without working unsubscribe aren’t eligible for mitigation.

Google Postmaster Tools has a compliance status dashboard that shows, for your primary domain, whether you meet each requirement: SPF and DKIM, DNS records, message formatting, encryption and spam rate for everyone, plus DMARC, one-click unsubscribe and honoring unsubscribes for bulk senders. The dashboard is part of Postmaster Tools v2; Google says the old Domain and IP Reputation dashboards will be retired.

What may come next: Google’s FAQ says “It’s likely that DMARC alignment with both SPF and DKIM will eventually be a sender requirement.” It gives no date.

Yahoo sender requirements

Yahoo’s Sender Hub lists almost the same rules. Enforcement began in February 2024.

All senders:

• SPF or DKIM at a minimum.
• A spam rate below 0.3%.
• Valid forward and reverse DNS for sending IPs.
• Mail that complies with RFC 5321 and RFC 5322.

Bulk senders, in addition:

• SPF and DKIM, and a DMARC policy of at least p=none that passes. Relaxed alignment is fine; the From domain must align with the SPF or the DKIM domain.
• A working List-Unsubscribe header with one-click unsubscribe for marketing and subscribed messages, plus a visible unsubscribe link in the body. Yahoo accepts the mailto: method and “highly recommends” the RFC 8058 POST method.
• Honor unsubscribes within 2 days.

Three differences from Gmail: Yahoo doesn’t publish a number of messages that makes you a bulk sender, its requirements list doesn’t mention TLS, and it calculates the spam rate on mail delivered to the inbox.

Outlook.com requirements for high-volume senders

Microsoft announced rules for high-volume senders in April 2025 on its Tech Community blog. The binding text is in the Outlook.com postmaster policies:

• Who: domains sending more than 5,000 emails a day to Outlook.com accounts.
• Since when: “Effective May 5th, 2025”.
• What: SPF and DKIM must pass, and DMARC must be in place: at least p=none (Microsoft recommends p=reject), aligned with SPF or DKIM, ideally both.
• Enforcement: the policies page says non-compliant messages from high-volume senders go to the junk folder and may be rejected if the problems aren’t fixed. Microsoft’s announcement was updated before the deadline to say that failing messages are rejected from May 5, 2025, and its support page for the error says Microsoft “now enforce[s]” the rules. The rejection reads:

550; 5.7.515 Access denied, sending domain [SendingDomain] does not meet the required authentication level.

For all senders, the policies require valid reverse DNS records for sending servers and an unsubscribe mechanism that is “clearly documented and easy for recipients to find and use”, say a sender must stop sending to a recipient after multiple non-delivery responses, and point to two free Microsoft services for managing your reputation: the Junk Email Reporting Program (JMRP) and Smart Network Data Services (SNDS).

Gmail, Yahoo and Outlook.com side by side

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Checklist

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Meeting the requirements gets you accepted; it doesn’t get you into the inbox on its own. The email deliverability guide covers reputation, list quality and content.

Sources

All checked October 29, 2026:

• Google: Email sender guidelines, Email sender guidelines FAQ, Gmail SMTP errors and codes, Postmaster Tools dashboards, Postmaster Tools v2, Google Workspace developer release notes
• Yahoo: Sender Hub best practices, Sender Hub FAQ, Introducing Insights (October 27, 2025)
• Microsoft: Outlook.com postmaster policies, practices and guidelines, announcement on Microsoft Tech Community, Fix NDR error 550 5.7.515
• RFC 8058: signaling one-click functionality for list email headers