It's a common point of confusion: does the SPF record on my domain affect the emails I receive? The short answer is that an SPF record's primary job is to authenticate your outbound email, not filter your inbound mail. However, the SPF system as a whole is a critical component of how modern mail servers, including your own, decide which incoming emails to trust.
Let's break down what that means. An SPF (Sender Policy Framework) record is essentially a public list of all the servers you have authorized to send email on behalf of your domain. When you send an email, the recipient's mail server can check this list to verify the message came from a legitimate source.
This process is designed to prevent bad actors from spoofing your domain, which is when they send malicious emails that appear to come from you. As Email on Acid explains, SPF lets receiving servers confirm a message is from an authorized source, making spoofing much more difficult.
How your SPF record influences inbound filtering for others
When you send an email, the receiving server performs an SPF check. This check directly influences its inbound filtering decisions for your message. Here is how it generally works:
- Email received: A mail server, like Gmail or Microsoft 365, receives an email claiming to be from your domain.
- SPF lookup: The server extracts the domain from the email's return-path address and looks up its SPF record in the DNS.
- IP address check:It compares the IP address of the server that sent the email against the list of authorized IPs in your SPF record.
- Filtering decision: If the IP address is on the list (an SPF 'Pass'), the email is seen as more trustworthy. If it is not on the list (an SPF 'Fail'), the server sees this as a strong negative signal. This failed check significantly increases the chance that the email will be sent to the spam folder or rejected outright.
So, your SPF record is a critical instruction for other systems on how to filter emails sent by you. It doesn't tell your own mail server how to filter emails sent by other people.
The role of SPF checks in your own inbound filtering
While your domain's SPF record doesn't control your inbound mail flow, your mail server absolutely uses SPF checks to filter the mail it receives from other domains. Almost every modern email security and spam filtering system performs SPF checks on all incoming messages. As noted by N-able, it's standard practice for inbound messages to be subject to an SPF check.
This is why having a correct SPF record yourself is so important. When your server checks an incoming email, it expects the sending domain to have a valid SPF record. In the same way, other servers expect you to have one. An incorrect or missing SPF record makes your domain look untrustworthy and can cause significant email deliverability problems.
In conclusion, your SPF record is an outbound tool that has a direct impact on inbound filtering at the recipient's end. It tells the world who can send email as you, and receiving servers use that information to filter out potential spam and phishing attacks. While it doesn't filter your own incoming mail, your server uses the same SPF mechanism to protect your users from malicious senders.
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