--- title: What Is an SPF Mechanism? description: Explanation of an SPF mechanism and what it does. --- [Skip to content](https://knowledgebase.mxtoolbox.com/home/what-is-an-spf-mechanism#main-content) [Request Support](https://knowledgebase.mxtoolbox.com/home/kb-tickets/new?hsLang=en) [![](https://knowledgebase.mxtoolbox.com/hs-fs/hubfs/logo.gif.png?width=110&height=27&name=logo.gif.png)](https://mxtoolbox.com/) - [Help Knowledgebase](https://knowledgebase.mxtoolbox.com/home/) - [Delivery Center Home](https://delivery.mxtoolbox.com/) - [Monitoring Home](https://mxtoolbox.com/monitoring) - [DMARC Knowledgebase](https://mxtoolbox.com/DMARC/knowledgebase) - [Status Page](https://mxtoolbox.statuspage.io/) Open main navigation Close main navigation - [Help Knowledgebase](https://knowledgebase.mxtoolbox.com/home/) - [Delivery Center Home](https://delivery.mxtoolbox.com/) - [Monitoring Home](https://mxtoolbox.com/monitoring) - [DMARC Knowledgebase](https://mxtoolbox.com/DMARC/knowledgebase) - [Status Page](https://mxtoolbox.statuspage.io/) - [Request Support](https://knowledgebase.mxtoolbox.com/home/kb-tickets/new) How can we help you? - There are no suggestions because the search field is empty. 1. [MxToolbox Help Center](https://knowledgebase.mxtoolbox.com/home?hsLang=en) 2. [Delivery Center](https://knowledgebase.mxtoolbox.com/home/delivery-center?hsLang=en) 3. [SPF Configuration & Performance](https://knowledgebase.mxtoolbox.com/home/delivery-center?hsLang=en#spf-configuration-performance) # What Is an SPF Mechanism? ## This article explains what an SPF mechanism is and what it does. An SPF (Sender Policy Framework) mechanism is a rule inside your domain's SPF DNS record that tells receiving mail servers which systems are allowed to send email on your behalf. These rules help mailbox providers verify legitimate senders and block spoofed or phishing messages. You can think of SPF as a guest list for your domain—only approved senders are allowed in. ### How SPF Works 1. **SPF record in DNS:** You publish an SPF record as a DNS TXT record for your domain. 2. **Authorization rules:** The record contains mechanisms that list approved sending IPs or services. 3. **Inbound checks:** When an email is received, the mail server looks up your SPF record. 4. **Verification:** The sending server's IP is checked against the SPF mechanisms to determine whether it's authorized. ### Common SPF Mechanisms - **`include:`** Authorizes another domain's SPF record (e.g., a third-party email service). - **`a`** Checks the domain's A or AAAA records for allowed IPs. - **`mx`** Authorizes the servers listed in the domain's MX records. - **`ip4:` / `ip6:`** Allows specific IPv4 or IPv6 addresses or ranges. - **`exists:`** Confirms whether a domain resolves to any IP address. - **`ptr:`** Uses reverse DNS lookups (rarely used and generally discouraged). - **`all`** Acts as a final rule, defining how to treat senders not explicitly allowed. ### SPF Qualifiers (Actions) Each mechanism can use a [qualifier](https://knowledgebase.mxtoolbox.com/home/what-is-an-spf-qualifier?hsLang=en) to tell receivers how to handle matches: - **`+` Pass** – Authorized sender - **`?` Neutral** – No policy decision (not recommended) - **`~` SoftFail** – Suspicious, often sent to spam - **`-` Fail** – Unauthorized, often rejected ### Why SPF Matters By clearly defining who can send email for your domain, SPF helps reduce spam, phishing, and spoofing—while improving deliverability for legitimate email. - [Delivery Center](https://knowledgebase.mxtoolbox.com/home/delivery-center?hsLang=en#main-content) - [Getting Started](https://knowledgebase.mxtoolbox.com/home/delivery-center?hsLang=en#getting-started) - [Domain Summary](https://knowledgebase.mxtoolbox.com/home/delivery-center?hsLang=en#domain-summary) - [Verified Sources](https://knowledgebase.mxtoolbox.com/home/delivery-center?hsLang=en#verified-sources) - [Integrations](https://knowledgebase.mxtoolbox.com/home/delivery-center?hsLang=en#integrations) - [SPF Configuration & Performance](https://knowledgebase.mxtoolbox.com/home/delivery-center?hsLang=en#spf-configuration-performance) - 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