How Does an SPF Record Work?

October 14, 2022

7 Min Read

Emails are an inevitable part of modern business. Companies use them for internal communications, sales, marketing, customer care, and whatnot. However, this communication method comes with significant risks and cyberthreats.

Hackers can misuse your domain name to gain the trust of targeted recipients by sending fake emails in your company’s name. These phishing, spoofing, and fraudulent emails are often used to scam people into divulging banking credentials, performing money transfers, and unwittingly installing malware onto their systems.

Fortunately, the problem can be averted by using email authentication and protection protocols like SPF, DKIM, and DMARC. In this blog, we focus on how SPF works and, more specifically, how SPF records work.

If you don’t already know about the Sender Policy Framework, check out our primer on the subject: What is SPF?

Otherwise, read about the return path, SPF record syntax, and how the SPF authentication process works.

What is a Return-Path?

Understanding the return-path is crucial to learning how email SPF works.

A return path (or reverse path) is a hidden email header that tells recipient servers where to send and how to process bounced emails. It consists of a separate SMTP address that senders use to specify where notifications for failed emails are sent.

This way, your inbox isn’t clogged with ‘failed delivery’ emails and bounced emails are kept organized.

Why is the Return-Path Important?

The return path (also known as a bounce address) is a safeguard that helps protect your email deliverability and sending reputation. It’s important for all email senders but more crucial to those who regularly send bulk emails.

Email campaigns are essential to any marketing strategy, but bounced emails aren’t uncommon. Instead of flooding your primary inbox with ‘failed delivery’ messages, the return path allows them to be stored and processed separately.

A return path address also helps validate a sender’s identity, thus improving sending reputation and deliverability rates.

How Does the Return Path Work With SPF?

The return path on its own indicates where bounced emails should go. When a recipient server gets an email, it checks whether the sending domain has SPF, DKIM, and DMARC protocols. If not, any fraudulent and spam emails can land in a recipient’s inbox.

With the SPF protocol, an email is validated using the return-path domain. If the sending server’s IP address and the return-path’s IP address don’t match, SPF authentication fails. However, an email can still pass SPF, even if the visible ‘From’ address is fake.

That’s where DKIM and DMARC come in. The former ensures that messages aren’t altered during transit, while the latter builds on both DKIM and SPF.

DMARC uses the ‘From’ field to verify the authenticity of an email. Your return-path email domain must match your part listed in the ‘From’ field. If it doesn’t, DMARC compliance isn’t possible, and fraudsters can still impersonate your domain.

Some email service providers allow you to set your return-path, while others set it up automatically.

What are Mechanisms, Qualifiers, and Modifiers?

How does SPF work with DNS records? Well, an SPF record details the authorized senders of a domain and instructs recipient servers on handling authentic and unverified emails. It has three significant elements: SPF Qualifiers, SPF Mechanisms, and SPF Modifiers that form part of SPF record syntax.

SPF Mechanisms

Mechanisms are used to instruct recipient servers on how to deal with each email purporting to come from your domain. There are eight types of mechanisms:

ALL
A
IP4
IP6
MX
PTR
EXISTS
INCLUDE

SPF Qualifiers

Understanding what SPF record is and how it works includes knowing about Qualifiers, an optional prefix to the above Mechanisms. Qualifiers are essential as they tell recipient mail servers how to process emails that don’t match a Mechanism value.

SPF Modifiers

Modifiers decide how SPF works for your domain by specifying its operating parameters. It includes name or value pairs separated by the ‘=’ symbol to highlight details.

The Steps of The SPF Process

So, how does SPF work in practical terms? Here’s a quick rundown of the process:

The server of a particular IP address sends an email and has set a return path (for example, [email protected]).
The recipient’s mail server checks the return-path address to find the domain and pull up that domain’s DNS records. In this case, it’d look for ‘example.com’ and then locate the SPF record.
If the recipient’s server finds the SPF record for ‘example.com,’, it’ll move to the next step; otherwise, SPF authentication fails.
Next, it’ll verify if any IP addresses enlisted as authentic senders in the SPF record match the sender’s email address. If so, SPF authentication passes. If no match is found, SPF authentication fails.
In case of SPF failure, the receiving server perceives the email as suspicious and typically rejects its entry into the recipient’s mailbox.

How to Place an SPF Record on Your Domain

You now know about the, process but how does email SPF work with DNS records? Below you’ll find the steps to place an SPF record on your domain. Remember, you must regularly check your SPF record after implementation to maintain its integrity and keep it updated.

Here’s what you need to do:

Understand Your Return-Path

Find out what return path your domain is using. You can get it by looking at your email header. If you want to set up a custom return path on your own domain (instead of using your ESP’s default return path), then you’ll have to implement SPF yourself.

Create Your SPF Record

When you create an SPF record, you’ll need to list all the sending sources and IP addresses permitted to send emails using your domain. A domain can have only one SPF TXT record, so all authorized senders must be listed in the same record. Don’t make the common mistake of creating a new record, as it can cause SPF authentication to fail.

Update your Domain’s DNS Settings

To add an SPF record to your DNS, log into your hosting provider account and go to your domain’s DNS settings. Follow the instructions to create a new DNS record and select the TXT record type. Add ‘@’ in the ‘Host’ field and add the SPF record in the ‘Value’ field.

This part can be tricky, but you can generate your SPF record and configure it correctly using the tools you’ll find at EasyDMARC.

You’re done!

Summary

SPF adds a security layer to your email domain, preventing phishing, scamming, and spoofing. It uses the return path, a hidden email header that directs where and how bounced emails will be processed, to verify the authenticity of an email.

Knowing how SPF works means understanding the SPF record and its three major elements: SPF Qualifiers, SPF Mechanism, and SPF Modifiers. The process is important too, but creating your SPF record and implementing it correctly is paramount.

You can use our enhanced EasySPF tool to ensure your domain allows only sources that you’ve actually authorized. If you have any trouble or need help solving SPF errors like the”Too many DNS lookups” issue, feel free to reach out to EasyDMARC.