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SMTP Bounce Code 5.2.2: Mailbox Full (Permanent)

SMTP bounce code 5.2.2 indicates that the recipient's mailbox has exceeded its storage quota and the condition is considered permanent. Unlike the temporary 4.2.2 bounce, this code suggests the mailbox is unlikely to be cleared and should be treated as a hard bounce.

What Does 5.2.2 Mean?

The enhanced status code 5.2.2 follows the SMTP Enhanced Status Code format:

  • 5 = Permanent failure (hard bounce)
  • 2 = Mailbox status (related to the recipient's mailbox)
  • 2 = Mailbox full (permanent condition)

When you receive a 5.2.2 bounce, it means the recipient's mailbox has been full for an extended period and the email provider has determined it's unlikely to be cleared. This is treated as a permanent failure, similar to other hard bounces.

Bounce Type

  • Type: Hard bounce (permanent failure)
  • Category: Mailbox
  • Action Required: Remove the email address from your mailing list

Common Causes

  1. Abandoned Account: The recipient has abandoned their email account and isn't checking or clearing it
  2. Inactive User: The recipient hasn't accessed their mailbox in a very long time
  3. Storage Limit Reached: The mailbox has reached its maximum storage capacity with no signs of being cleared
  4. Automated Email Accumulation: The account receives automated emails that accumulate without being read or deleted
  5. Shared Mailbox Neglect: In enterprise environments, a shared mailbox that no one is managing
  6. Account Owner Deceased: In rare cases, the account owner may be deceased and the mailbox is accumulating emails

How to Resolve

For Email Marketers

  1. Remove from Mailing List: Treat 5.2.2 bounces as permanent failures and remove addresses immediately
  2. Add to Suppression List: Add these addresses to a suppression list to prevent future sends
  3. Monitor for Reactivation: While unlikely, you can optionally monitor if the mailbox becomes active again
  4. Contact Recipient: If you have alternative contact information, reach out to verify if they want to clear their mailbox
  5. Review Engagement: Check if these recipients were previously engaged—if not, their removal may improve your metrics

For Developers

  1. Automated Removal: Set up automated processing to remove 5.2.2 bounces from your database
  2. Suppression List Management: Maintain a suppression list of permanently full mailboxes
  3. Distinguish from 4.2.2: Ensure your system correctly distinguishes between temporary (4.2.2) and permanent (5.2.2) mailbox full conditions
  4. Log Patterns: Track which recipients have permanently full mailboxes to identify inactive users
  5. Cleanup Processes: Implement periodic cleanup processes to remove permanently full mailboxes

Difference from 4.2.2

  • 4.2.2 (Temporary): Mailbox is full but may be cleared—retry sending
  • 5.2.2 (Permanent): Mailbox has been full for an extended period—remove from list

The key difference is that 4.2.2 suggests the condition is temporary and may resolve, while 5.2.2 indicates the condition is permanent and unlikely to change.

Related Bounce Codes

Examples

Example Bounce Message

550 5.2.2 Mailbox full
The recipient's mailbox is full and has been for an extended period.

Example Enhanced Status Code

550 5.2.2 <[email protected]>: Mailbox quota exceeded (permanent condition)

Common Email Provider Responses

  • Gmail: "Mailbox quota exceeded (permanent)"
  • Outlook/Hotmail: "550 5.2.2 Mailbox full"
  • Enterprise: "Mailbox permanently full"
  • Custom: "Quota exceeded - permanent condition"

Best Practices

  1. Remove Immediately: Treat 5.2.2 bounces as permanent failures and remove addresses immediately
  2. Don't Retry: Unlike 4.2.2, don't attempt to resend to permanently full mailboxes
  3. Maintain Suppression Lists: Keep a suppression list of permanently full mailboxes
  4. Identify Inactive Users: Use 5.2.2 bounces to identify inactive or abandoned accounts
  5. Improve List Quality: Removing permanently full mailboxes improves your list quality and engagement metrics
  6. Monitor Patterns: Track if certain segments have higher rates of permanently full mailboxes
  7. Respect User Status: If a mailbox has been permanently full, respect that the user is likely inactive