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SPF, DKIM, and DMARC authentication: How they work ...
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Setting up SPF, DKIM, and DMARC is one of the most effective ways to protect your domain from impersonation and phishing. Each of these protocols plays a different role in email authentication, and all of them need to be published in your domain’s DNS settings. “If you have access to your domain’s DNS and know which services send email on your behalf, you are ready to get started.” How to set up SPF