How SPF, DKIM and DMARC Work
SPF, DKIM and DMARC are complementary email authentication mechanisms.
SPF
SPF lists systems authorized to send for a domain. Maintain one valid SPF policy and include every legitimate sender.
DKIM
DKIM adds a digital signature that recipients verify through a public DNS key.
DMARC
DMARC evaluates alignment and tells recipients how to handle failures. Start with reporting, review legitimate sources and tighten policy gradually.
Also check rDNS
Self-managed mail servers should use a consistent hostname, forward DNS and PTR record.
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