How can DKIM selector errors create intermittent failures?

DKIM selector error patterns:

Selector mismatch:

Messages signed with selector not in DNS

DKIM fails because key not found

Can happen during key rotation

Intermittent causes:

Multiple sending systems with different selectors

Key rotation mid-process

Load balancer routing to different configs

DNS propagation during changes

Symptoms:

DKIM passes sometimes, fails others

Inconsistent authentication results

Confusion about what is wrong

Diagnosis:

Check DKIM-Signature header for selector used

Verify that selector exists in DNS

Check all sending paths

Ship using credentials not registered at some ports. Verify all credentials match all routes.