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SMTP Error 553: Mailbox Name Not Allowed

SMTP error 553 indicates that the requested action was not taken because the mailbox name is not allowed. This is a permanent failure that occurs when the email address format or mailbox name violates server policies.

What Does 553 Mean?

The SMTP reply code 553 follows the standard SMTP response format:

  • 5 = Permanent failure (permanent negative completion reply)
  • 53 = Requested action not taken: mailbox name not allowed

When you receive a 553 error, it means the mail server rejects the mailbox name because it violates server policies or restrictions. This is a permanent error that requires fixing the mailbox name.

Error Type

  • Type: Permanent failure (hard error)
  • Category: Mailbox name validation
  • Action Required: Fix the mailbox name or remove the address

Common Causes

  1. Invalid Characters: The mailbox name contains invalid characters
  2. Reserved Names: The mailbox name is reserved or restricted
  3. Policy Violation: The mailbox name violates server naming policies
  4. Format Issues: The mailbox name format is incorrect
  5. Blacklisted Names: The mailbox name is on a blacklist
  6. Length Limits: The mailbox name exceeds length limits
  7. Domain Restrictions: The domain portion violates restrictions
  8. Security Policy: Security policies prevent the mailbox name

How to Resolve

For Email Senders

  1. Verify Address Format: Verify that the email address format is correct
  2. Check for Typos: Check for typos or invalid characters in the address
  3. Contact Recipient: Contact the recipient to verify their email address
  4. Remove from List: Remove the address if it cannot be fixed
  5. Validate Before Adding: Validate email addresses before adding to your list

For Developers

  1. Validate Email Format: Use proper email validation before sending
  2. Check Server Policies: Understand server policies for mailbox names
  3. Error Handling: Handle 553 errors as permanent failures
  4. Address Validation: Implement comprehensive address validation
  5. Logging: Log 553 errors to identify problematic address patterns

Related SMTP Errors

Examples

Example Error Message

553 Requested action not taken: mailbox name not allowed

Example with Enhanced Status Code

553 5.1.3 Invalid mailbox name

Common Scenarios

  • Invalid Characters: "553 Mailbox name contains invalid characters"
  • Reserved Name: "553 Mailbox name is reserved"
  • Policy Violation: "553 Mailbox name violates server policy"

Best Practices

  1. Validate Before Sending: Always validate email addresses before sending
  2. Handle as Permanent: Treat 553 errors as permanent failures
  3. Remove Invalid Addresses: Remove addresses that result in 553 errors
  4. Use Validation Libraries: Use well-tested email validation libraries
  5. Log Patterns: Log 553 errors to identify problematic address patterns
  6. User Communication: Notify users when their addresses are invalid
  7. Prevent Collection: Prevent invalid addresses from being collected
  8. Regular Validation: Regularly validate addresses in your database