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.