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By implementing a policy in your DMARC record, you're telling mail servers all around the world how to handle unauthorized use of your company's email. You could strictly monitor email traffic (p=NONE), quarantine email traffic to be on the safe side (p=QUARANTINE), or completely reject all unauthorized messages (p=REJECT).
DMARC can be configured on all GlowHost plans with self-service options, or the GlowHost team can do it for you!