4.2.2 SMTP bounce: mailbox full
What 4.2.2 means
The recipient mailbox is over its quota. This is a transient condition, so the sender should retry later.
Message text
Mailbox full
Common causes of 4.2.2
- Recipient mailbox quota is full
How to fix 4.2.2
- Retry later; the queue does this automatically.
- If it persists, the recipient must free space.
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How to read 4.2.2
The second part, 4.2.2, is an enhanced status code (RFC 3463 §2) written class.subject.detail. Class 4 is a Persistent transient failure (4xx): the command was not accepted, but the condition may clear, so the sender should try again later (RFC 5321 §4.2.1; RFC 3463 §2).. Subject 2 is mailbox: a problem with the recipient mailbox, such as full, disabled or unknown. The detail number refines the subject, and providers may define details of their own, which is why one code can read differently at Gmail, Microsoft and Yahoo.
Sending servers should retry a deferred message. RFC 5321 §4.5.4.1 advises waiting at least 30 minutes between attempts and trying for at least 4 to 5 days before giving up and returning a bounce. If the deferral keeps repeating, fix the cause rather than waiting.
Official source: www.rfc-editor.org. Last verified 2026-10-20.
Related guides
- How to create an SPF record (syntax and examples)
- How DKIM works and how to publish a DKIM record
- How to set up a DMARC record, from p=none to p=reject
Related codes
- 421 SMTP: service not available
- 450 SMTP: mailbox unavailable
- 451 SMTP: local processing error
- 452 SMTP: insufficient storage
- 4.4.1 SMTP: no answer from host
- 4.7.0 SMTP: security status
FAQ
What does 4.2.2 mean?
The recipient mailbox is over its quota. This is a transient condition, so the sender should retry later. This is a temporary failure.
How do I fix 4.2.2?
Retry later; the queue does this automatically. If it persists, the recipient must free space.
Is 4.2.2 permanent, and should I retry?
4.2.2 is a temporary failure. Your mail server normally retries by itself; if it keeps repeating, fix the cause.