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What are DMARC, DKIM, and SPF? - Cloudflare
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Meanwhile, DMARC tells mail servers what to do when DKIM or SPF fail, whether that is marking the failing emails as "spam," delivering the emails anyway, or dropping the emails altogether. “Domains that have not set up SPF, DKIM, and DMARC correctly may find that their emails get quarantined as spam, or are not delivered to their recipients.” *A domain, roughly speaking, is a website address like "example.com". Domains form the second half of an email address: [email protected], for instance.
How does SPF work? “Sender Policy Framework (SPF) is a way for a domain to list all the servers they send emails from.” SPF records list all the IP addresses of all the servers that are allowed to send emails from the domain, just as an employee directory lists the names of all employees for an organization. Mail servers that receive an email message can check it against the SPF record before passing it on to the recipient's inbox.
DKIM and SPF can be compared to a business license or a doctor's medical degree displayed on the wall of an office — they help demonstrate legitimacy. “Meanwhile, DMARC tells mail servers what to do when DKIM or SPF fail, whether that is marking the failing emails as "spam," delivering the emails anyway, or dropping the emails altogether.” Domains that have not set up SPF, DKIM, and DMARC correctly may find that their emails get quarantined as spam, or are not delivered to their recipients. They are also in danger of having spammers impersonate them.