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A Layer of Protection in Email Infrastructure: Sender Policy Framework (SPF)

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Have you ever had someone grab your phone and text someone, pretending to be you (jokingly or maliciously)? Doesn't make you feel very wonderful. Even if you tell the recipient the truth, they'll probably be sceptical of all your texts in the future. You'll also probably be extra cautious about who you let borrow your phone. Trust has been shattered.

A similar scenario can occur in the realm of email, and would-be phishers don't require your account or password to impersonate your company. Isn't it terrifying?

Fortunately, we have a simple, not-so-secret method for safeguarding your brand's image. It's called Sender Policy Framework (SPF), and it's a lifesaver for email reputation.

The simple mail transfer protocol (SMTP) gets a message from the sender to the receiver when the email is transmitted from one server to another. Twilio SendGrid provides this operation as an SMTP service.

Whatever sender or host can identify themselves and their email as any domain they wish, which is a security flaw in the email system (kind of like how people have created TONS of Donald Trump Twitter accounts), this makes it harder for recipients to believe that a message is from whom it claims to be. It also makes senders uncomfortable to know that anyone can send email from their domain and perhaps harm their brand's reputation.

Recipients lose faith in email legitimacy, and senders are concerned that imposters are impersonating their brand— neither of which is good for anyone! The SPF record stored in a txt record in the DNS is one part of the solution. In this article, we'll go over everything there is to know about SPF, from what it is to how to find mistakes on your own.

What is an SPF Record?

Sender Policy Framework (SPF) is an acronym for Sender Policy Framework. It's an email authentication method for determining which mail servers can deliver email from a specific domain. ISPs can use this validation protocol to detect when spoofers and phishers attempt to deliver malicious emails to your subscribers by forging emails from your domain.

With SPF, recipients may be sure that the emails they receive are from the people they anticipate. Senders may relax knowing that phishers aren't impersonating or phishing their audience from their brand.

An SPF record is a single line of text added to a domain's txt record by the domain administrator in technical terms. Like the A, PTR, and MX records, the txt record is recorded in the DNS (domain name system). The following is an example of an SPF record:

“v=spf1 ip4: include:example.com -all”

How SPF works

The above line of text instructs the receiving SMTP server, which hosts are permitted to deliver mail from a specific domain.

The SPF record is often examined very early in the SMTP discussion before the message body is sent. A TCP connection is established between the sender and the receiving server when a message is attempted to be sent.

A HELO command is sent after the connection is established, telling the receiving server which domain is attempting to send it mail. This is followed by a MAIL FROM command, which informs the receiving server of the sender's email address. The domain utilised for the SPF record check is the domain discovered in the MAIL FROM (also known as the envelope from and return path)command.

The receiving server will now check the SPF record for the IP address of the SMTP client attempting to send the message. The message will pass SPF authentication if the IP address is listed.

The nitty-gritty: breaking down each piece of the SPF record

An SPF record is made up of various mechanisms, including:


A domain name is always followed by a period. When the receiving server encounters an include mechanism, it checks the domain's SPF record. The mail is authenticated, and the SPF check is completed if the sender's IP appears in that record. The SPF check moves on to the next mechanism if it isn't detected.


A domain name is also included. The SPF, on the other hand, checks for the IP address linked with that domain in this scenario. If it matches the sender's IP, the SPF check is completed. If this is not the case, it will proceed to the next mechanism.


In the same vein as “A.” A domain name is always added after it. If the domain listed corresponds to the IP address of the transmitting client, authentication is successful, and the SPF check is completed. If this is not the case, it will proceed to the next mechanism.

IP4 and IP6 are two types of the internet protocol.

A colon always follows a specified IP address or CIDR range. Authentication will pass, and the SPF check will be completed if the sending client's IP is mentioned after any IP4 or IP6 mechanism. If this is not the case, it will proceed to the next mechanism.

In SPF records, PTR should never be used. They are prone to errors and take a lot of memory and bandwidth to resolve for receiving servers for technical reasons. In addition, because of the presence of a PTR mechanism, some servers will fail SPF authentication.


It permits a domain administrator to point a domain to another domain's SPF record, even though it is strictly a modification and not a method. If the REDIRECT function is utilised, no additional mechanisms, including the “all” mechanism, can be included in the SPF record. “v=spf1 redirect:example.com” is an example of a redirect record.

There can only be ten of these because the “INCLUDE,” “A,” “MX,” “PTR,” “EXISTS,” and “REDIRECT” techniques all require DNS lookups. This appears straightforward enough, but it also includes nested DNS lookups, so an “INCLUDE” leads to another SPF record with two additional “INCLUDE” techniques that counts as three DNS lookups. They pile up quickly!

How do I check my SPF record?

Everyone doesn't use SPF authentication, but receivers that reject based on SPF failure will reject delivery. Rather than blocking mail that violates SPF, some recipients may place it in quarantine.

Each SPF record will be a bit different, but you should check to make sure you’ve got it right. Here are three tools that can help validate your records:

Scott Kitterman’s SPF Testing Tools:


SPF Record Check

SPF Wizard

Make Sender Policy Framework a priority

Malicious email messages, expressed, harm your business and damage the email channel. Phishers will be more likely to move on to easier targets if they see your Sender Policy Framework-protected domain. While SPF will not prevent spam, it will deter and reduce your vulnerability to attacks. I mean, who doesn't want that? As a result, we strongly advise all email clients to set up an SPF record.

When used in conjunction with Sender ID, DKIM, and DMARC, SPF adds an added layer of email security to your users' experience by assisting ISPs incorrectly identifying your email and, as a result, spammers.



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