What is SPF?

Sender Policy Framework (SPF) is used to authenticate the sender of an email. With an SPF record in place, Internet Service Providers can verify that a mail server is authorized to send email for a specific domain. An SPF record is a DNS TXT record containing a list of the IP addresses that are allowed to send email on behalf of your domain.

 

How does SPF work?

To take advantage of SPF, you publish an SPF record in the DNS. The record is a list of all the IP addresses that are allowed to send email on behalf of the domain. 

The SPF mechanism uses the domain in the return-path address to identify the SPF record. When a sender tries to hand-off an email to an email “receiving” server for delivery, the server checks to see if the sender is on the domain’s list of allowed senders. If so, then a link has been established between the piece of email and the email domain. If not, then the server continues processing the email as usual without this link, as any number of things could be going on. 

The email might be real, but the list of senders might not be accurate. Real email might have been forwarded which means the email could have come from anywhere and the list of allowed senders doesn’t help too much. Or, the email is fake and unwanted. Too many possible outcomes makes it difficult to attach meaning to the absence of the link that SPF can provide. DKIM fills the gap in the DMARC technical framework as an additional way to try and link a piece of email back to a domain.

 

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SPF and DMARC for Email

By itself, SPF can associate a piece of email with a domain. With the DNS records in place, DMARC ties the results of SPF to the content of email, specifically to the domain found in the return path or From: header of an email. For SPF to work correctly in the context of DMARC, the return-path address has to be relevant to the domain of the From: header, which is the item that ties together DMARC alignment.

 

Why is SPF Important?

SPF has become exceedingly vital to help verify which sending infrastructure can relay email on behalf of your domain. Implementing SPF for email provides major benefits:

 

  • Increases domain reputation and email deliverability.
  • Fights domain impersonation and email spoofing to protect your brand reputation.
  • One of the foundational methods of email authentication for DMARC.

 

Information here has been copied from https://dmarcian.com/why-dmarc/