Mailbox provider sender requirements

Since 2024, the major mailbox providers publish hard requirements for bulk senders — authentication, one-click unsubscribe, spam-rate ceilings. Miss one and your mail is filtered no matter how good the content is. These pages track each provider's current rules, and every page carries the date we last verified it against the provider's own documentation.

• Gmail sender requirements: what Google enforces for bulk emailLast reviewed: 2026-08-20

  The 5,000-a-day rule, the 0.3% spam ceiling and one-click unsubscribe — Gmail's sender guidelines, verified against Google's own documentation.

• Outlook sender requirements: Microsoft's rules for high-volume emailLast reviewed: 2026-08-20

  Since May 2025, Outlook.com filters unauthenticated bulk mail and then rejects it — SPF, DKIM and DMARC or error 550 5.7.515.

• Yahoo sender requirements: authentication, complaints and the feedback loopLast reviewed: 2026-08-20

  Yahoo never names a volume threshold — authentication, the 0.3% spam-rate ceiling and complaint handling decide instead.