Setting up Sender Policy Framework (SPF) is a foundational step for email deliverability and security. Usually, when I'm helping someone configure their SPF record, the first place I look is the documentation provided by their Email Service Provider (ESP). These guides typically lay out the exact include statements or IP addresses needed to authorize their sending infrastructure.
However, what happens when that documentation is nowhere to be found, or it's incomplete or misleading? It's a common, frustrating scenario where ESPs might mention sender authentication without actually providing the necessary SPF details. This guide will walk you through setting up SPF when you're left without clear instructions from your ESP, ensuring your emails are authenticated and reach the inbox.
Before diving into the setup process, it's essential to grasp the fundamentals of SPF. SPF, or Sender Policy Framework, is an email authentication method designed to prevent sender spoofing and reduce spam. It allows domain owners to specify which mail servers are authorized to send emails on their behalf. When a receiving mail server gets an email, it checks the SPF record in the sender's DNS to verify that the email originated from an authorized IP address.
An SPF record is published as a TXT record in your domain's DNS. It starts with v=spf1, indicating the SPF version. Following this, you add various mechanisms like a, mx, ip4, and include to specify authorized senders. The record concludes with an all mechanism, which defines the policy for unauthorized senders.
Understanding these components is crucial because it allows you to construct an SPF record manually, even when your ESP doesn't provide explicit instructions. The goal is to accurately list all legitimate sending sources for your domain.
Identifying your sending sources
The biggest challenge without ESP documentation is figuring out which servers are actually sending email on your behalf. The first step is to compile a comprehensive list of every service that sends email using your domain. This includes your primary email provider (e.g., Google Workspace or Microsoft 365), your marketing automation platform, transactional email services, and any other third-party tools that send notifications or messages from your domain.
One effective method for discovery is to check the email headers of messages sent from your domain. Look for the Received headers, which often reveal the IP addresses and hostnames of the servers that handled the email. This can give you clues about the include mechanisms or IP addresses you need. However, manually inspecting headers can be tedious and prone to missing sources.
A far more robust approach is to leverage DMARC reports. If you have DMARC enabled, these reports provide comprehensive insights into all IP addresses and domains sending mail on behalf of your domain, including those you might not even be aware of. They will show you exactly which sources are passing or failing SPF and DKIM authentication. This is an invaluable tool for discovering all legitimate (and illegitimate) sending sources, especially when your ESP is not providing the necessary information. For more information, check out our guide on understanding and troubleshooting DMARC reports.
Using DMARC reports for SPF discovery
DMARC reports are a goldmine for SPF setup without ESP documentation. They provide aggregate data on who is sending email purporting to be from your domain. If you do not have DMARC configured, you can use our free DMARC record generator tool to get started. Be sure to start with a p=none policy initially to avoid deliverability issues. Once you begin receiving reports, you can use a DMARC monitoring service to easily parse and analyze the XML data, revealing all your sending IPs and domains. This will highlight any unauthorized senders or missing SPF records.
Constructing the SPF record
Once you have identified all your legitimate sending sources, it's time to build your SPF record. Remember, you can only have one SPF TXT record per domain. If you already have one, you'll need to merge the new mechanisms into the existing record. The record must start with v=spf1. For each third-party service, you'll typically use an include mechanism, such as include:spf.example.com. If you're sending from specific IP addresses, use ip4 or ip6 mechanisms.
It's important to be mindful of the 10-DNS-lookup limit for SPF records. Each include, a, mx, and ptr mechanism counts as a lookup. Exceeding this limit can cause SPF validation failures, leading to emails being rejected or sent to spam. If you're using multiple ESPs, this limit can be tricky to manage. Learn how to address this challenge in our guide on troubleshooting SPF authentication issues with multiple ESPs.
The final part of your SPF record is the all mechanism, which determines the policy for servers not explicitly listed. There are two common qualifiers: ~all (softfail) and -all (hardfail). ~all suggests that unauthorized emails might still be legitimate and should be accepted but marked with a softfail. -all strictly instructs receiving servers to reject any email from unauthorized sources. While -all offers stronger protection, it's safer to start with ~all to avoid accidentally blocking legitimate emails, especially if you're unsure if all sending sources have been identified. You can transition to -all once your SPF record is fully validated through DMARC reports.
For web hosting providers that might have undocumented includes, such as websitewelcome.com, DMARC reports are your best bet. These reports can reveal IPs that are failing SPF because they are not included in your record, helping you identify what needs to be added. This is often the case with providers like Bluehost or HostGator where the cPanel or WHM setup might not be comprehensive. Once you know the necessary include or IP, you add it to your SPF record.
Testing and monitoring your SPF record
After constructing your SPF record, it's crucial to test it before publishing it to your DNS. Tools exist online that can help you validate your SPF record's syntax and ensure it doesn't exceed the 10-lookup limit. This preliminary check can save you from potential email delivery issues. Remember that SPF is a critical component of email authentication, and errors can lead to your emails being flagged as spam or outright rejected. If your emails are still going to spam, check out our guide on why your emails are going to spam.
Once published, ongoing monitoring is essential. This is where DMARC reports become indispensable once again. They provide continuous feedback on your SPF (and DKIM) authentication status. By analyzing these reports, you can quickly identify if new sending sources are appearing that need to be added to your SPF record, or if there are any issues with your existing configuration. This proactive monitoring helps maintain your email deliverability and prevents your domain from being added to a blacklist (or blocklist).
Should you encounter SPF authentication failures, DMARC reports will point you to the problematic IP addresses or sending domains. Common issues include exceeding the 10-lookup limit or simply missing an include. Regularly reviewing your DMARC aggregate reports via a DMARC monitoring service ensures that your SPF record remains accurate and effective, even without direct guidance from your ESP.
Views from the trenches
Best practices
Always leverage DMARC reports to identify all sending IPs and domains, especially when ESP documentation is scarce.
Start with a relaxed SPF policy (~all) and monitor DMARC reports before moving to a stricter (-all) policy.
Consolidate multiple SPF records into a single TXT entry to avoid validation failures and DNS lookup issues.
Periodically review your SPF record and DMARC reports to account for changes in your email infrastructure.
Common pitfalls
Exceeding the 10-DNS-lookup limit, which leads to SPF validation failures.
Creating multiple SPF TXT records for a single domain, which is invalid and causes errors.
Not including all legitimate sending sources, resulting in emails from those sources failing SPF checks.
Misinterpreting DMARC reports or failing to use them for ongoing SPF optimization.
Expert tips
If an ESP doesn't provide SPF includes, look for common patterns in their IP ranges or reverse DNS.
Some ESPs use non-standard terms like 'sender authentication' instead of 'SPF'.
Directly ask your ESP's support for their exact SPF requirements if documentation is missing.
If your web host uses a cPanel/WHM setup, verify their suggested SPF as it can sometimes be incorrect or incomplete.
Marketer view
Marketer from Email Geeks says: Clients often struggle with SPF setup when ESP documentation is absent or unclear, making it hard to provide specific recommendations.
2023-01-13 - Email Geeks
Marketer view
Marketer from Email Geeks says: Some ESPs support SPF but use non-standard terminology, like 'sender authentication' instead of 'SPF', which complicates finding relevant information.
2023-01-13 - Email Geeks
Next steps for your SPF setup
While having clear ESP documentation for SPF setup is ideal, its absence doesn't have to be a roadblock to proper email authentication. By systematically identifying your sending sources, understanding SPF syntax, and leveraging the power of DMARC reports, you can build and maintain an effective SPF record. This proactive approach not only helps you overcome documentation gaps but also ensures robust email security and optimal deliverability, keeping your emails out of the spam folder and off critical blacklists.
