TL;DR
Mailbox full: no unchanged retry; capacity can change, so do not automatically suppress.
What this code means
X.2.2 means a full mailbox caused by an administrative quota or physical capacity. The recipient may free space; 5.2.2 combines this condition with permanent class 5.
Provider examples
554 5.2.2 mailbox full;
STOREDRV.Deliver.Exception:QuotaExceededException.MapiExceptionQuotaExceeded552 5.2.2 The email account that you tried to reach is over quota. Please direct the recipient to https://support.google.com/mail/?p=OverQuotaPerm - gsmtp552 5.2.2 The recipient's inbox is out of storage space and inactive. Please direct the recipient to Manage files in your Google Drive storage. - gsmtpsmtp;552 5.2.2 The email account that you tried to reach is over quota. Please direct the recipient to https://support.google.com/mail/?p=OverQuotaPerm - gsmtp552 5.2.2 <example@icloud.com>: user is overquotaTechnical meaning
This is a mailbox-capacity condition, not proof that the address is invalid. Microsoft’s accepted response is a provider example of mailbox full.
Delivery status
Class 5 is permanent for the unchanged request, even though the capacity state can later change.
- Class
- Permanent failure
- Retry
- Do not retry unchanged
- Suppression
- Check the full context
Retry decision
Stop retries until the recipient or administrator confirms that capacity was freed or the quota changed.
Suppression decision
Do not automatically suppress the address or domain from 5.2.2 alone; use full context and policy.
Read more
Common causes
- The recipient exceeded mailbox quota or available physical capacity.
Diagnostic steps
- Confirm the exact code, recipient, and attempt time, then request confirmation of a capacity change.
Actions by owner
Sender
- Stop unchanged retries and share the exact response with the recipient.
Recipient
- Free space where possible or ask the administrator for help.
Recipient administrator
- Inspect quota, usage, and logs; confirm the new state before advising a retry.
Sources
These sources define what this enhanced status code means, mainly through the IANA registry and related RFCs. When provider examples appear on the page, they come from that provider's published documentation. Follow the links to read the original wording in context.
- SMTP Enhanced Status Codes — IANA registry of enhanced mail system status codes.
- RFC 5248 — A Registry for SMTP Enhanced Mail System Status Codes — Creates and governs the IANA enhanced status code registry.
- RFC 2034 — SMTP Service Extension for Returning Enhanced Error Codes — Defines how SMTP returns enhanced status codes to clients.
- RFC 3463 — Enhanced Mail System Status Codes — Defines the class/subject/detail model for enhanced status codes.
- NDR error 554 5.2.2 mailbox full for public folders — Microsoft Learn article on mailbox-full NDRs for mail-enabled public folders.
- smtp-codes (community corpus) — Community-maintained reference of provider SMTP responses, pinned locally as evidence.
- Gmail SMTP errors and codes — Official Gmail Help table of SMTP error messages and status codes.
- SMTP Field Manual (community corpus) — Community-maintained reference of provider SMTP responses, pinned locally as evidence.
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