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SMTP Bounce Code 4.2.2: Mailbox Full

SMTP bounce code 4.2.2 indicates that the recipient's mailbox has exceeded its storage quota and cannot accept new messages. This is a soft bounce (temporary failure), meaning you should retry sending the email later.

What Does 4.2.2 Mean?

The enhanced status code 4.2.2 follows the SMTP Enhanced Status Code format:

  • 4 = Persistent transient failure (soft bounce)
  • 2 = Mailbox status (related to the recipient's mailbox)
  • 2 = Mailbox full (quota exceeded)

When you receive a 4.2.2 bounce, it means the recipient's mailbox has reached its storage limit. Unlike hard bounces, this is typically a temporary condition—once the recipient clears space in their mailbox, they can receive emails again.

Bounce Type

  • Type: Soft bounce (persistent transient failure)
  • Category: Mailbox
  • Action Required: Retry sending after a delay (typically 24-48 hours)

Common Causes

  1. Storage Quota Exceeded: The recipient's mailbox has reached its storage limit set by the email provider
  2. Inactive Account: The recipient hasn't checked their email in a long time, causing the mailbox to fill up
  3. Large Attachments: Previous emails with large attachments have consumed the available storage space
  4. Email Hoarding: The recipient keeps all their emails without deleting old messages
  5. Shared Mailbox: In enterprise environments, a shared mailbox may have reached its quota limit

How to Resolve

For Email Marketers

  1. Retry Strategy: Implement an automated retry mechanism that attempts to resend the email after 24-48 hours
  2. Monitor Retry Attempts: Don't retry indefinitely—if the mailbox remains full after 3-5 attempts, consider it a persistent issue
  3. Contact Recipient: If possible, reach out to the recipient through alternative channels to inform them about the full mailbox
  4. Segment Affected Recipients: Create a segment for recipients with full mailboxes and pause sending until they clear space
  5. Review Sending Frequency: Consider reducing email frequency for recipients who consistently have full mailboxes

For Developers

  1. Implement Retry Logic: Set up exponential backoff retry logic for 4.2.2 bounces
  2. Track Retry Count: Monitor how many times you've retried sending to addresses with full mailboxes
  3. Set Retry Limits: Define a maximum number of retry attempts (typically 3-5) before marking as failed
  4. Log Bounce Patterns: Track which recipients frequently have full mailboxes to identify patterns
  5. Automated Cleanup: After multiple failed retries, automatically pause sending to these addresses

Retry Strategy

For 4.2.2 bounces, implement a retry schedule:

  • First retry: 24 hours after initial bounce
  • Second retry: 48 hours after first retry
  • Third retry: 72 hours after second retry
  • Final attempt: 1 week after third retry

If the mailbox remains full after all retry attempts, consider removing the address from your active list or marking it as inactive.

Related Bounce Codes

Examples

Example Bounce Message

452 4.2.2 Mailbox full
The recipient's mailbox is full and cannot accept new messages.

Example Enhanced Status Code

452 4.2.2 <[email protected]>: Mailbox quota exceeded

Common Email Provider Responses

  • Gmail: "Mailbox quota exceeded"
  • Outlook/Hotmail: "452 4.2.2 Mailbox full"
  • Yahoo: "Mailbox temporarily full"
  • Enterprise: "Quota exceeded for mailbox"

Best Practices

  1. Don't Give Up Immediately: Unlike hard bounces, 4.2.2 bounces are temporary—retry sending
  2. Respect Retry Limits: Don't retry indefinitely; set a maximum number of attempts
  3. Monitor Patterns: Track recipients who frequently have full mailboxes
  4. Educate Recipients: Include information in your emails about managing mailbox storage
  5. Consider Alternative Channels: For important communications, consider using alternative contact methods if the mailbox remains full