Login

SMTP Bounce Code 5.1.0: Other Address Status

SMTP bounce code 5.1.0 indicates that there is an addressing problem with the recipient's email address that doesn't fit into a more specific category. This is a permanent failure (hard bounce), meaning the address has a fundamental issue that won't resolve on retry.

What Does 5.1.0 Mean?

The enhanced status code 5.1.0 follows the SMTP Enhanced Status Code format:

  • 5 = Permanent failure (hard bounce)
  • 1 = Addressing status (related to the recipient address)
  • 0 = Other or undefined addressing status

When you receive a 5.1.0 bounce, it means the receiving mail server has identified an addressing problem that doesn't fall into specific categories like "user unknown" (5.1.1) or "invalid domain" (5.1.2). This is a catch-all code for various addressing issues.

Bounce Type

  • Type: Hard bounce (permanent failure)
  • Category: Addressing
  • Action Required: Remove the email address from your mailing list or investigate the specific addressing issue

Common Causes

  1. Address Format Issues: The email address format is problematic but doesn't match other specific error codes
  2. Local Part Problems: Issues with the local part (before @) of the email address that don't match syntax errors
  3. Address Policy Violations: The address violates the recipient domain's addressing policies
  4. Alias Issues: Problems with email aliases or forwarding configurations
  5. Mailbox Restrictions: The address has restrictions that prevent delivery
  6. Virtual Mailbox Configuration: Issues with virtual mailbox table configurations
  7. Address Validation Failure: The address failed validation checks on the receiving server
  8. Domain-Specific Rules: Address violates domain-specific addressing rules
  9. Quota Exceeded on Creation: Address-related quota issues that prevent mailbox creation
  10. Generic Addressing Error: An addressing error that doesn't fit into more specific categories

How to Resolve

For Email Marketers

  1. Remove from List: Remove the email address from your active mailing list immediately
  2. Verify Address Format: Double-check the email address format for any obvious issues
  3. Validate Address: Use email validation tools to verify the address format
  4. Contact Recipient: If possible, contact the recipient through alternative channels to verify their correct email address
  5. Review Collection Methods: Review how you collected this email address to prevent similar issues
  6. Clean Your List: Regularly clean your email list to remove invalid addresses

For Developers

  1. Validate Email Format: Implement comprehensive email format validation before storing addresses
  2. Implement Bounce Handling: Set up automated bounce processing to remove 5.1.0 bounces from your database
  3. Use Email Verification Services: Consider using email verification APIs to check addresses before sending
  4. Log Bounce Details: Log the full bounce message to understand the specific addressing issue
  5. Pattern Analysis: Analyze 5.1.0 bounces to identify patterns and improve validation
  6. Address Normalization: Implement address normalization to catch format issues early
  7. Suppression List: Maintain a suppression list of bounced addresses

Investigation Steps

When you receive 5.1.0 bounces, investigate:

  1. Check Full Bounce Message: Review the complete bounce message for specific details about the addressing issue
  2. Validate Address Format: Verify the email address follows proper format ([email protected])
  3. Test Address: Try sending a test email to verify the issue
  4. Check Domain: Verify the domain portion of the address is correct
  5. Review Collection Source: Understand where the address was collected to identify potential issues

Related Bounce Codes

Examples

Example Bounce Message

550 5.1.0 Other address status
Address does not meet recipient domain policies.

Example Enhanced Status Code

550 5.1.0 <[email protected]>: Other address status - address validation failed

Common Email Provider Responses

  • Generic: "550 5.1.0 Other address status"
  • Policy Violation: "Address does not meet domain policies"
  • Validation Failure: "Address validation failed"
  • Format Issue: "Address format problem"

Best Practices

  1. Never Retry: Don't attempt to resend emails to addresses that bounce with 5.1.0—they will continue to fail
  2. Validate Before Adding: Always validate email addresses before adding them to your mailing list
  3. Use Double Opt-in: Implement double opt-in to ensure email addresses are valid
  4. Maintain List Hygiene: Regularly clean your email list to remove invalid addresses
  5. Investigate Patterns: Analyze 5.1.0 bounces to identify common issues and improve validation
  6. Log Bounce Details: Keep detailed logs of bounce messages to understand specific issues
  7. Use Suppression Lists: Maintain suppression lists to prevent sending to invalid addresses