Mailbox full
A delivery failure because the recipient's mailbox has reached its storage limit, reported with enhanced status code 4.2.2 or 5.2.2.
What it means
RFC 3463 defines X.2.2 as mailbox full: the user has exceeded a per-mailbox administrative quota or the physical capacity. Servers report it as a temporary failure (452 4.2.2), which the sender retries, or as a permanent one (552 5.2.2) when they do not expect it to clear soon.
A full mailbox is usually treated as a soft bounce, because the address exists and may empty again. A mailbox that stays full for weeks may well be abandoned: Gmail's 552 5.2.2 text describes the account as full and inactive. Amazon SES does not count mailbox-full failures toward its bounce rate.
Related terms
On this site
Sources
What this definition rests on. The wording is ours; the facts are theirs.
- RFC 3463, section 3.3: Mailbox Statusrfc-editor.org
- IANA, SMTP Enhanced Status Codes registryiana.org
- Google Workspace Admin Help: Gmail SMTP errors and codesknowledge.workspace.google.com
- Amazon SES Developer Guide: Enforcement FAQs (bounce rate)docs.aws.amazon.com
All 432 terms in the glossaryThe wiki: blocklists and bounce codes