Understanding SPF records

SPF stands for Sender Policy Framework - a protocol used to prevent spammers from sending messages with forged ‘From’ addresses at your domain.

An SPF Record is a type of TXT record which identifies any mail servers permitted to send email on behalf of your domain - they are sometimes known as Reverse MX records.

Domain administrators publish SPF records in the DNS, so they can be used by incoming mail servers to verify the domain name from which email messages are sent. When a recipient's mail server receives an email message, it checks the SPF record to determine whether it is a valid message. If the message comes from a server that is included in the SPF record, it is legitimate; if not, it is rejected as spam.

How an SPF record works.

Do I have to update the SPF record?

No. However, it’s worth noting that some recipient domains may reject messages from users if they cannot validate that they have been sent from an authorized mail server.

How do I update the SPF record?

Updating SPF records needs to be done by a domain administrator. The exact process will vary from one service provider to another, but it is essentially just a matter of adding one line to a DNS TXT record. For example:

v=spf1 mx ip4: include:spf.protection.outlook.com include:spf.exclaimer.net ~all

Can I have multiple SPF records?

Multiple SPF records are not recommended as this can cause issues with delivery and/or spam classification.


If you’re interested in a little more background information about SPF records, this section may be useful.

As noted previously, SPF records are a type of DNS record, so it is useful to start with an understanding of DNS and the context of SPF.

Domain Name System (DNS)

DNS is the short form for Domain Name System, a system that is used to identify and organize Web domains. It can be helpful to think of DNS as the equivalent of a telephone directory for the Web, allowing network communication services to look up names and translate them into Internet Protocol (IP) addresses. DNS information is gathered from all the domain name servers across the Internet and stored at the Central Registry - hosting companies and Internet Service Providers interact with this registry on a regular basis to obtain updated DNS information.

So, at a basic level, when you type www.exclaimer.net into a web browser, DNS is used to look up this address and establish which IP address should be used to make a connection and display the web page.

Things get a little more complicated when we start to look at how email is sent and received. Again, a DNS lookup is required, but we need to delve a bit deeper and look at DNS records. The DNS includes different types of records which are used for specific purposes. For this article, we are interested in two particular types: MX and TXT.

MX records

MX records are resource records within the DNS which specify a mail server which is responsible for accepting email messages on behalf of a recipient's domain, together with a preference value which is used to prioritize delivery if multiple mail servers are available.

All domains publish MX records so we know what servers can receive email for the domain. So, when an email is sent, the sending mail server looks up the MX record in the DNS to obtain the relevant IP address.

Text (TXT) records

A TXT record is a DNS record that provides text information to sources outside your domain; it can be used for many different purposes, one of which is SPF. So, when we refer to SPF records, we are referring to a particular type of TXT record within the DNS.

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