What happens when DNS fails mid-transaction?

DNS failure mid-transaction disrupts delivery in progress:

When it can happen:

Initial MX lookup succeeds. Connection established to mail server. Additional DNS needed (SPF check, reverse lookup). That secondary lookup fails.

Typical outcomes:

Soft failure: 4xx code, message queued for retry. Connection drop: Transaction abandoned. Partial processing: Some recipients succeed, others fail.

Common scenarios:

SPF lookup timeout during authentication check. PTR lookup failure for reverse DNS check. Network instability affecting DNS.

Handling:

Usually treated as temporary. Automatic retry should succeed. Persistent failures indicate infrastructure issues.

Mid-transaction DNS failure is losing the map partway through the journey. Usually temporary; retry and proceed.