A sender policy framework (SPF) functions like an event guard stationed in your lobby. You provide a guest list, and the guard welcomes those with names on the list while everyone else waits for approval or gets turned away.
For example, a small business owner usually knows customers and suppliers by name, and you've seen their company logos, personnel, and other identifiers. However, email exchanges lack those visual cues of legitimacy.
The VP of Marketing for a medium-sized company may only know a handful of customers and suppliers by sight. So, instead, the VP relies on a receptionist to screen calls and visitors, only allowing those whose concerns cannot be delegated to junior staff members to speak directly.
In contrast, the CEO or owner of an international import/export company might only speak to someone scheduled well in advance. Moreover, anyone permitted to have an appointment must also have a concern vital to the entire company that only the CEO can handle, such as a VIP customer with a complicated contract.
In each of these situations, businesses must have some way to distinguish the genuine sender. Otherwise, your company could suffer a significant loss of reputation if a spammer, scammer, or bot impersonated you and gained access to your customer list or email server. Your sender policy framework provides that distinguishing factor.
Learn more about SPFs, including answers to your questions such as "What is an SPF record" and "How do you create an SPF record?", so you can leverage this security measure for your own company.
What are sender policy framework records?
An SPF record is essentially a digital ID verification system for your emails. It's a specific line of text (TXT) code added to your domain's DNS records that works behind the scenes to authenticate email senders and ensure they're coming from authorized IP addresses.
When properly configured, this record tells receiving email servers that the email comes from legitimate sources authorized to send emails from certain domains.
SPF authentication works by creating a list of approved IP addresses and server names that are permitted to send emails using your domain. When someone receives an email claiming to be from your domain, their email server automatically checks this SPF record to verify the sending server is on your approved list.
Here's how each element works:
- Sender identification: The SPF record allows recipient servers to confirm an email truly originated from an authorized source and not from someone attempting to spoof your domain. This verification happens invisibly during email delivery.
- Sender verification: Email systems can automatically check if the sending mail server's IP address matches what's listed in your SPF record, preventing unauthorized servers from successfully impersonating your domain in emails.
- Return path verification: SPF provides a trusted route back to the authentic source if recipients have questions about your message or concerns about how their information is being used, enhancing accountability.
By implementing SPF records, you're essentially telling the world exactly which servers are allowed to send emails on your domain's behalf, creating a crucial first layer of email security and sender authentication.
Limitations of SPF: What SPF can't do
While sender policy framework records help domain owners secure their email communications, this email authentication protocol has limitations that are important to understand. SPF isn't a complete security solution on its own.
Its limitations include:
- No encryption capabilities: When receiving mail servers perform SPF authentication, they only verify sender authenticity but do nothing to protect the actual content of your messages. Anyone who intercepts your emails can still read them if you're not using additional encryption.
- No privacy features: These records don't hide email metadata or protect sensitive information within your messages. They simply verify that an email comes from an authorized mail server.
- Breaks when forwarded: When someone forwards your email, the SPF validation fails because the forwarder's sending server's IP address becomes the new sender. This means legitimate forwarded messages may get flagged as suspicious.
- No reporting functionality: Unlike more advanced protocols, SPF doesn't generate reports about who's trying to spoof your domain or provide analytics on delivery issues related to authentication.
- Insufficient as a standalone solution: The DNS lookup performed during SPF checks is just one layer of email security. Smart attackers can find ways around SPF-only protection, which is why experts recommend implementing it alongside DKIM and DMARC for comprehensive protection.
- Limited protection scope: SPF only verifies the sending server, not the actual content of emails. This means phishing attacks with malicious content can still pass SPF checks if sent from authorized servers.
What do you need to know about SPF?
Implementing sender policy framework records tells recipient email servers that your message isn't spoofing, spamming, or attempting to scam them. By taking the time to incorporate SPF records into your domain settings, you create a verification process that increases confidence and decreases resistance to your messages.
When messages claim to come from your SPF-protected domain but originate from unauthorized servers, they'll fail SPF authentication checks, protecting both your brand reputation and your recipients from potential scams.
This verification system is especially important for handling incoming mail, as it provides an additional layer of security screening before messages reach inboxes.
Key points to understand about SPF include:
- IP address verification: An SPF record is essentially a published list of IP addresses authorized to send emails on behalf of your domain, giving clear instructions to email providers about handling your outgoing messages.
- Delivery improvement: Your SPF record provides a layer of protection that makes your legitimate messages more likely to reach the intended receiver's inbox rather than being flagged as spam.
- No encryption function: While SPF verifies sender authenticity, it doesn't encrypt your message content or provide privacy protection for the information within.
- Header visibility: SPF verification results appear in the full headers of your email messages, allowing recipients to manually check authentication if needed.
- Trust signaling: The SPF domain listed first in your "include" mechanism demonstrates you've taken the minimum precautions to protect both your business data and your recipients from potential email-based threats.
SPF vs. DMARC vs. DKIM
The Internet Engineering Task Force published the current SPF protocol in RFC 7208 in April 2014. The purpose was to create a consensus on keeping hackers and phishers from sending emails that supposedly come from a known, trusted organization.
That consensus became spf1, and from that point forward, v=spf1 became the standard format for the beginning statement of every SPF record. However, forwarding a message invalidates the SPF. Consequently, two additional strategies have come into play: DKIM and DMARC.
What is DKIM?
DKIM is an acronym for DomainKeys Identified Mail. Like SPF, DKIM is a TXT record in the DNS. However, DKIM records remain valid even when forwarded. Current DKIM standards arose from efforts by Yahoo! and Cisco, who each created their own email authorization standards.
Think of DKIM as the wax seal once applied to official documents. These wax seals were recognizable; if a message arrived with a missing or broken seal, it was not considered trustworthy.
Every dispatching email server has a two-part DKIM: the private DKIM key and a public key. Every receiving server accesses the public half of that key. The receiving email server performs a lookup in the DNS txt record when you send your email message.
If that email server finds your public DKIM key, it opens the DKIM signature. If the signature in the message matches the signature you published in your DNS, the receiving email server considers that message valid. If not, that message bounces, which means it does not reach the intended receiver's inbox.
Instead, it might not get delivered, go to the spam folder, or go to whatever other folder the user has set up to deal with such messages.
The correct format for DKIM records looks like this: