How can split-brain DNS cause email delivery problems?

Split DNS email problems:

Authentication inconsistency:

Internal SPF check passes (internal DNS shows authorized IP)

External receiver queries public DNS (different result)

Authentication fails unexpectedly

MX routing confusion:

Internal MX points to internal server

External sender cannot reach internal server

Mail delivery fails or times out

Testing confusion:

Tests from inside network succeed

External senders report failures

Hard to reproduce problems

DKIM verification:

If DKIM selector resolves differently, signature verification fails

Keep email authentication records consistent between internal and external DNS.

Conflicting instructions between harbor offices cause delivery to the wrong dock or failed verification.