DIAGNOSTIC PLAYBOOK
Mailbox full: when to retry and when to review
A mailbox-capacity response points to a recipient-side condition, but the exact SMTP class determines how the sending system should treat the attempt. Preserve the full response rather than mapping every capacity message to one universal retry rule.
HealthCheck Email editorial team · · Examples are illustrative
How to investigate
- Read the primary and enhanced response codes together with the diagnostic text.
- Let the sending platform apply its documented retry behavior for temporary replies.
- Review persistent failures through your contact-maintenance process and use another channel when appropriate.
What this looks like
ILLUSTRATIVE EXAMPLE
A destination temporarily defers because a mailbox is full. Changing your SPF record does not create space in the recipient's mailbox.
A mistake to avoid
A friendly error label in a dashboard may hide the actual response class. Use the original response when deciding whether an unchanged retry is appropriate.
Keep the result in context
A successful handoff, a delivered event and an inbox placement are different observations. Record the receiving provider, send time, SMTP response and affected stream before comparing results. DNS fixes address authentication or routing; they cannot establish consent or guarantee placement.
Take the next step
Use the related check to gather evidence, then compare it with the affected message or service. Keep the result and time with your notes so a later change can be distinguished from the original problem.
Sources and further reading
The protocol references below explain the underlying behavior. Your sending or DNS provider supplies the account-specific settings for its service.