Bulk sender requirements

Bulk sender requirements are the enforcement rules major mailbox providers apply to high-volume senders, generally those sending 5,000 or more messages per day to a provider. They were formalized by Gmail and Yahoo in 2024 and echoed by Microsoft for Outlook.com in 2025. The core requirements: authenticate with SPF and DKIM, publish a DMARC policy, keep spam complaint rates under 0.3%, support one-click unsubscribe, and maintain valid forward/reverse DNS. They turned long-standing best practices into hard gates.