SMTP 4.2.2: recipient mailbox is full

RFC 3463mailbox_fullaction: retry

4.2.2 means the recipient's mailbox is over quota. It is temporary and the address is still valid, so retry. If it persists for several days the mailbox is likely abandoned and should be suppressed.

What it looks like in the log

452 4.2.2 The email account that you tried to reach is over quota.

452 4.2.2 Mailbox full

552 5.2.2 Over quota

Why it happens

• The recipient is not reading or clearing their mail.
• An abandoned mailbox that is still accepting connections.

What to do

• Retry on the normal backoff schedule for a few days.
• Suppress after a sustained period. A permanently full mailbox is an unengaged recipient and often becomes a spam trap.
• Note the 5.2.2 variant is permanent: same meaning, different verdict.

Related

5.1.1 · 5.2.1

Classified as mailbox_full, action retry. Paste a response into the bounce classifier to check one against the same ruleset.

Written and maintained by Rastu Singh, an infrastructure engineer working on high-volume email in Tallinn.