SPF, DKIM, DMARC

The acronyms refer to standards and techniques to make the mailing safer, for example declaring which server is allowed to send an email for a specific domain or to sign the content of an email to verify its validity.

All those techniques are applied at the server level, specifically to the mail server, with the support of specific entries in the DNS.

All those systems cannot be controlled by the Newsletter plugin.

If you use a delivery service (Amazon SES, Mailgun, Sendgrid, Mailjet, …) it provides instructions to configure the SPF and the DKIM. The DMARC is a bit more sophisticated and usually managed directly by the provider.

SPF

The SPF is the simple one, it is just an entry in your DNS used to declare which servers can send emails for a specific domain. It is usually set up even by the hosting provider to indicate the webserver as an allowed sender for the hosted domain. You can ask your provider about the SPF DNS record.

If the provider set up the record only for their mailing service (when the provider gives you one or more mailboxes and the SMTP parameters), you probably should add to your blog an SMTP plugin and connect it with the provided SMTP service.

Read more on Wikipedia.

DKIM

DKIM is a signature add to emails. It is usually added by the service that delivers the email (your provider or by the delivery service you are using).

DKIM requires an entry in the DNS used by the receiver to verify the signature it finds inside the message. Some email clients show a “Signed By” when they find the signature and it is valid.

Usually hosting providers do not offer DKIM, while delivery services do. Sometimes special configuration is needed, sometimes it is fully managed by the delivery service.

You can even find plugins that add the DKIM signature to mail sent from a WordPress blog. This is prone to fail since the mail server (where the signature should be added) can change/reencode the parts of the email making the signature no more valid. Be warned.

Read more on Wikipedia.

DMARC

DMARC is a standard for communication between the sending server and the receiving one. It is used, for example, to report when a user marks an email as spam. Delivery services already manage it but they can offer the option to configure the DMARC on your own domain (not that easy).

Read more on Wikipedia.

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