Temporary — will retry
SMTP 452 4.2.2
insufficient storage, mailbox full
SMTP 452 4.2.2 means the recipient's mailbox is over its storage quota, returned as a temporary failure so the sending server retries. Unlike the permanent 552 form, this one explicitly invites a later attempt, and mail often arrives once the recipient clears space.
How it appears
452 4.2.2 Mailbox size limit exceeded
452 4.2.2 <user@example.com>: Recipient address rejected: mailbox full
452 4.2.2 Over quota
What causes it
- The recipient has exceeded their storage allocation.
- A shared or role mailbox has grown past its quota with nobody clearing it.
- The receiving server itself is low on disk and is deferring all mail.
How to fix it
In order — try the first one first.
- Allow the automatic retries to run — the address itself is valid.
- If it persists across weeks, suppress the address. A permanently full mailbox is abandoned, and abandoned mailboxes are what become recycled spam traps.
- If every recipient at one domain returns it, the problem is the server rather than the mailboxes, and there is nothing you can do from your side.
Common questions
- What does SMTP 452 4.2.2 mean?
- SMTP 452 4.2.2 means the recipient's mailbox is over its storage quota, returned as a temporary failure so the sending server retries. Unlike the permanent 552 form, this one explicitly invites a later attempt, and mail often arrives once the recipient clears space.
- Should I retry a 452 4.2.2 error?
- Yes, and your sending server does it automatically. 452 is a temporary deferral, and legitimate mail usually arrives on a retry within minutes or hours. Only investigate if it persists across many retries.
- How do I fix SMTP 452 4.2.2?
- Allow the automatic retries to run — the address itself is valid.
Last reviewed 2026-09-11