Login

SMTP Bounce Code 4.4.1: No Answer From Host

SMTP bounce code 4.4.1 indicates that the destination mail server did not respond to the connection attempt. This is a soft bounce (temporary failure), meaning the server may be temporarily unavailable and you should retry sending the email later.

What Does 4.4.1 Mean?

The enhanced status code 4.4.1 follows the SMTP Enhanced Status Code format:

  • 4 = Persistent transient failure (soft bounce)
  • 4 = Network and routing status
  • 1 = No answer from host

When you receive a 4.4.1 bounce, it means the mail server tried to connect to the destination server but received no response. This is typically a temporary network or server issue that should resolve itself.

Bounce Type

  • Type: Soft bounce (persistent transient failure)
  • Category: Network/Routing
  • Action Required: Retry sending after a delay (typically 30 minutes to a few hours)

Common Causes

  1. Server Down: The destination mail server is temporarily down or offline
  2. Network Issues: Temporary network connectivity problems between mail servers
  3. DNS Problems: Temporary DNS resolution issues preventing connection to the host
  4. Firewall Blocking: Temporary firewall rules blocking the connection
  5. Server Overload: The destination server is overloaded and not accepting connections
  6. Maintenance: The destination server is undergoing maintenance
  7. Timeout: Connection timeout due to network latency or server unresponsiveness
  8. Routing Issues: Temporary routing problems preventing the mail server from reaching the destination

How to Resolve

For Email Marketers

  1. Retry Strategy: Implement an automated retry mechanism that attempts to resend the email after 30 minutes to 2 hours
  2. Monitor Retry Attempts: Retry multiple times as this is often a temporary issue
  3. Check Delivery Status: Monitor delivery reports to see if retries succeed
  4. Segment Affected Domains: Track which domains frequently have no-answer issues
  5. Contact Support: If a specific domain consistently fails, contact the recipient's IT department

For Developers

  1. Implement Retry Logic: Set up retry logic with shorter intervals (30 minutes to 2 hours) for 4.4.1 bounces
  2. Connection Timeout Configuration: Configure appropriate connection timeouts in your mail server
  3. DNS Caching: Implement DNS caching to reduce DNS lookup issues
  4. Monitor Connection Patterns: Track which hosts frequently don't respond to identify patterns
  5. Exponential Backoff: Use exponential backoff for retries, but with shorter initial delays than other soft bounces
  6. Health Checks: Implement health checks to monitor destination server availability

Retry Strategy

For 4.4.1 bounces, implement a retry schedule with shorter intervals:

  • First retry: 30 minutes after initial bounce
  • Second retry: 1 hour after first retry
  • Third retry: 2 hours after second retry
  • Fourth retry: 4 hours after third retry
  • Final attempt: 24 hours after fourth retry

These shorter intervals are appropriate because server availability can change quickly.

Related Bounce Codes

Examples

Example Bounce Message

451 4.4.1 No answer from host
Connection timeout or host not responding.

Example Enhanced Status Code

451 4.4.1 <[email protected]>: No answer from host example.com

Common Email Provider Responses

  • Generic: "451 4.4.1 No answer from host"
  • Timeout: "Connection timeout - host not responding"
  • Network Error: "Unable to connect to destination server"
  • DNS Error: "DNS resolution failed for host"

Best Practices

  1. Retry Sooner: Unlike other soft bounces, 4.4.1 issues can resolve quickly, so retry sooner
  2. Monitor Server Status: Track which servers frequently don't respond
  3. Check Network Connectivity: Ensure your mail server has proper network connectivity
  4. DNS Configuration: Ensure DNS servers are properly configured and responsive
  5. Connection Pooling: Use connection pooling to improve connection reliability
  6. Timeout Configuration: Set appropriate connection timeouts to avoid hanging connections
  7. Log Connection Issues: Log connection failures to identify patterns or problematic hosts