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SMTP Bounce Code 5.6.0: Other Media Error

SMTP bounce code 5.6.0 indicates that there is a problem with the message content, media type, or message format that doesn't fit into a more specific category. This is a permanent failure (hard bounce), meaning there's a fundamental issue with the message content that prevents delivery.

What Does 5.6.0 Mean?

The enhanced status code 5.6.0 follows the SMTP Enhanced Status Code format:

  • 5 = Permanent failure (hard bounce)
  • 6 = Message content or media status
  • 0 = Other or undefined media error

When you receive a 5.6.0 bounce, it means the receiving mail server has identified a problem with the message content, media type, or format that doesn't fall into more specific categories. This is a catch-all code for various content-related issues.

Bounce Type

  • Type: Hard bounce (permanent failure)
  • Category: Content/Media
  • Action Required: Fix the message content/format or remove the email address from your mailing list

Common Causes

  1. Unsupported Media Type: The message contains media types that the server cannot handle
  2. Content Format Issues: Message content format problems that don't match other specific errors
  3. Encoding Problems: Character encoding issues that prevent content processing
  4. Attachment Issues: Problems with attachments that don't fit other categories
  5. MIME Format Errors: MIME format issues that prevent proper parsing
  6. Content Policy Violations: Message content violates policies but doesn't match other rejection codes
  7. Media Conversion Failure: Server cannot convert or process the message media
  8. Content Size Limitations: Message content exceeds size limitations (though this may also result in other codes)
  9. Character Set Issues: Character set problems that prevent content display or processing
  10. Generic Content Error: A content error that doesn't fit into more specific categories

How to Resolve

For Email Marketers

  1. Review Message Content: Review the message content, attachments, and format for issues
  2. Simplify Message Format: Simplify message format to use standard, widely-supported formats
  3. Check Attachments: Verify attachments are in supported formats and properly encoded
  4. Fix Encoding Issues: Ensure proper character encoding (UTF-8 recommended)
  5. Remove Problematic Content: Remove or fix problematic content that may cause errors
  6. Test Message Format: Test message format before sending to large lists
  7. Remove from List: If unable to fix the content issue, remove the address from your mailing list

For Developers

  1. Validate Message Format: Implement message format validation before sending
  2. Check MIME Structure: Verify MIME structure is valid and follows standards
  3. Validate Media Types: Ensure media types are supported and properly declared
  4. Fix Encoding: Use proper character encoding (UTF-8) for all text content
  5. Attachment Handling: Properly encode and format attachments according to standards
  6. Implement Bounce Handling: Set up automated bounce processing to handle 5.6.0 bounces
  7. Log Content Errors: Log content errors to identify patterns and problematic content
  8. Message Validation: Validate message content against common mail server requirements

Investigation Steps

When you receive 5.6.0 bounces, investigate:

  1. Check Full Bounce Message: Review the complete bounce message for specific content details
  2. Review Message Content: Examine the message content, attachments, and format
  3. Verify Encoding: Check character encoding and character sets used
  4. Test Message Format: Test the message format with different mail servers
  5. Check Attachments: Verify attachments are properly formatted and encoded
  6. Review MIME Structure: Ensure MIME structure follows RFC standards

Related Bounce Codes

Examples

Example Bounce Message

550 5.6.0 Other media error
Message content format is not supported.

Example Enhanced Status Code

550 5.6.0 <[email protected]>: Other media error - unsupported content format

Common Email Provider Responses

  • Generic: "550 5.6.0 Other media error"
  • Format Error: "Message content format not supported"
  • Media Type: "Unsupported media type in message"
  • Encoding Error: "Character encoding error in message content"

Best Practices

  1. Use Standard Formats: Always use standard, widely-supported message formats
  2. Proper Encoding: Use UTF-8 encoding for all text content
  3. Valid MIME Structure: Ensure MIME structure follows RFC standards
  4. Supported Media Types: Use media types that are widely supported
  5. Proper Attachment Encoding: Properly encode attachments using base64 or quoted-printable
  6. Test Before Sending: Test message format before sending to large lists
  7. Validate Content: Validate message content against common requirements
  8. Log Content Issues: Log content errors to identify patterns and improve message formatting

Technical Details

Message Format Standards

Message formats are defined in:

  • RFC 5322: Internet Message Format
  • RFC 2045-2049: MIME (Multipurpose Internet Mail Extensions)
  • RFC 3676: Text/Plain Format and DelSp Parameters

Common Content Issues

  • Invalid MIME structure
  • Unsupported media types
  • Encoding problems
  • Character set issues
  • Attachment format errors
  • Content size limitations

Resolution Strategies

  1. Standard Formats: Use standard message formats (text/plain, text/html, multipart/alternative)
  2. UTF-8 Encoding: Use UTF-8 for all text content
  3. Valid MIME: Ensure MIME structure follows RFC 2045-2049
  4. Proper Attachments: Use base64 encoding for binary attachments
  5. Content Validation: Validate content before sending
  6. Testing: Test messages with various mail servers and clients