What does “temporary deferral” mean in logs?

A temporary deferral (or soft bounce with retry) indicates the receiving server couldn't accept the message right now but might accept it later. The message stays queued for automatic retry.

• Common deferral reasons:
• Rate limiting: "Too many connections" or "sending too fast." The recipient is throttling your volume.
• Server busy: Temporary overload or maintenance on the receiving end.
• Greylisting: Intentional first-attempt rejection to filter spam (legitimate retries succeed).
• Reputation-based delays: Provider is delaying your mail due to questionable reputation without outright blocking.
• Temporary filtering: Content triggered a filter that defers rather than rejects.
• What happens next:
• ESP queues the message
• Retries according to backoff schedule
• Most deferrals resolve within hours
• Persistent deferrals (days) may eventually bounce
• When to be concerned:
• High deferral rates to a specific domain (they might be throttling you)
• Growing deferral queues (delivery not keeping up)
• Deferrals converting to bounces after retry exhaustion

Deferrals are normal in small numbers. Large-scale deferrals suggest you need to slow down, improve reputation, or investigate recipient-side issues.