What 552 Mailbox quota exceeded Means
552 is a permanent failure on the receiver's storage quota. Per RFC 5321 §4.2.3, the requested action wasn't taken because the receiver's storage allocation is full. Most often this is the recipient mailbox at its quota limit, but can also be a message-size limit (552 5.3.4 or 552 5.2.3).
Most receivers when a recipient genuinely is over quota. Microsoft 365, Gmail (rarely; usually 552 5.2.2 or 552 5.2.3 with enhanced codes), and self-hosted servers. Many enterprise receivers also use 552 for message-size-limit rejections.
Recipient hasn't cleaned out their inbox and is over the per-mailbox storage quota set by their IT admin; or the message you sent exceeds the receiver's per-message size limit (typically 25-50 MB for major providers).
How to Fix 552 Mailbox quota exceeded
- 1
Read the enhanced status code if present
552 5.2.2 = recipient mailbox full. 552 5.2.3 = message exceeds receiver's max size. 552 5.3.4 = message too large for receiver. These three have very different fixes.
- 2
If recipient mailbox full — don't keep retrying
If 5.2.2, the recipient needs to free space. You can't fix that. Some sending platforms suppress addresses after 2-3 consecutive 5.2.2 events. The address may become deliverable again in days or weeks; auto-suppression with periodic re-validation is the typical strategy.
- 3
If message too large — shrink it
Cold email rarely triggers size limits (a 50KB cold email is normal). If you're seeing 5.2.3 / 5.3.4, you're likely sending unnecessary large attachments or embedded images. Strip them. Most cold email doesn't need attachments — link instead.
- 4
Audit large attachments in your sequence templates
If multiple recipients across different domains return 552 5.2.3, your sequence templates contain a too-large file. Check the campaign for any attached files; replace them with a link to a cloud-hosted file.
References
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- ◇RFC 1870 — SMTP Service Extension for Message Size Declaration
Defines the SIZE extension and message-size handling.
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552 Mailbox quota exceeded in the Cold Email Context
552 is mostly noise for cold email — your messages are short, attachments are rare, and recipient over-quota is something you can't fix. But it does signal something useful: prospects who chronically hit 552 5.2.2 either don't manage their inbox or have left the role. If your sending platform's suppression policy doesn't auto-pause repeat-552 addresses, you're spending sends on contacts who functionally don't read mail. ColdRelay's bounce classification flags repeat-552 addresses so they're excluded from future campaigns until they re-validate.
Frequently Asked Questions
Should I retry 552?
Short-term: yes if you have queue lifetime remaining (RFC 5321 suggests retrying transient-looking failures). Long-term: no, 5xx is permanent. Most platforms convert 552 to a soft suppression after a few attempts, allowing the address to re-enter rotation after a recovery window (1-7 days).
What's the typical mailbox quota limit?
Varies widely. Gmail consumer: 15 GB shared. Outlook.com free: 15 GB. Microsoft 365 Business Basic: 50 GB per mailbox. Google Workspace: 30 GB - unlimited. Smaller / self-hosted: often 2-10 GB. Quotas exhaust gradually over years.
Is 552 5.2.2 the same as 452?
Similar cause (storage), different severity. 452 is transient (try later); 552 is permanent (give up). Some receivers escalate 452 to 552 after persistent retries fail.
Will a smaller message bypass 552?
Only for 552 5.2.3 / 5.3.4 (message-size). For 552 5.2.2 (recipient quota), message size doesn't matter — the recipient's mailbox is full and won't accept any message regardless of size.