SMTP Error 550 5.1.1

What This Error Means

This error indicates that the recipient email address is invalid or does not exist on the mail server. The mailbox may have been deleted, never existed, or contains a typo. This is a permanent failure and the email will not be delivered.

Common Causes

• 1The email address was typed incorrectly
• 2The recipient's mailbox has been deleted or deactivated
• 3The domain exists but the specific user does not
• 4The email was sent to an old address that no longer exists

How to Fix It

• 1Verify the email address spelling with the recipient
• 2Remove the address from your mailing list immediately
• 3Use email verification services like Whylidate to validate addresses before sending
• 4Implement double opt-in to ensure valid addresses at signup