SMTP 552 mailbox full: interpret the complete storage failure

Define the decision

A mailbox-full explanation is different from a nonexistent recipient. It also does not override the server’s actual status class. Avoid a rule that labels every 552 response retryable simply because storage can change later.

Work through the procedure

1. Capture the basic code, enhanced code and full human-readable response.
2. Separate recipient mailbox quota from message-size or system-storage limits.
3. Follow the application’s documented failure classification and provider guidance.
4. If a reviewed retry is appropriate, preserve the original attempt and a bounded decision window.

Worked example

The following is a synthetic example for this procedure, not a customer result or performance benchmark.

Observed response: 552 5.2.2 mailbox full
Evidence: permanent-class response with a quota explanation
Decision: do not place it into an unconditional automatic retry loop
Review: provider guidance and contact-handling policy

Read the result

The distinction matters when a sending tool has already suppressed the address. An operator should understand that state before trying another campaign or changing a lead record.

Check before moving on

1. Check attachment size if the response concerns message size.
2. Verify no duplicate attempt was already accepted.

Limits and next action

Do not treat an old full-mailbox response as permission to contact indefinitely. Keep retries intentional, limited and consistent with the recipient’s other suppression signals.

Source: RFC 3463: mailbox status distinctions