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Deferral

Email Deliverability. A deferred status can occur when an ISP or mailbox provider can't to accept email from your IP address. The provider then waits for the resent message.

Twilio SendGrid retries delivering a deferred message for 72 hours from the time of the first deferral.

  • If the resent message succeeds, the provider determines that can trust you as a sender or their system operations return to normal, it accepts the message.
  • If the resent message fails, Twilio places the email address on the Block Suppression list.

Possible causes

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  • The receiving server doesn't recognize your IP address and may think you're sending spam. IP warmup familiarizes recipient mail servers with your sending habits and later anticipate your messages.
  • The receiving server lacks open ports to receive email.
  • The recipient's mailbox is full.
  • Some recipients have marked your mail as spam, but not enough to block you. The recipient server refuses to receive more email messages from you until they can learn more about how their users interact with your messages.