What are the SPF records?

SPF records (Sender Policy Framework Records) are a special type of TXT records in a zone file of a domain name, which can be used to indicate which smtp server is used to send your emails.

SPF records were initially created with the ultimate goal of protecting users from domain spoofing. Due to the fact that the SMTP protocol does not have a built-in mechanism to check the validity of the "From Address" header in emails, the SPF record and the other identification records (DKIM, DMARC) prevent the use of our domain by unauthorized users.

How SPF records work?

When sending an email, a user - the sender of the message - communicates with another user - the recipient of the message. In between, there is a test. The incoming mail server used by the receiver asks the DNS to check whether the IP address from which the message was sent is identified with any of the IP addresses specified by the SPF records made for the sender's domain.

The result of the test gives a value to the Received - SPF variable, which exists in the email header. This variable can take one of the following 4 possible values:

-pass
-neutral
-softfail
-fail

Depending on the value of the variable and the settings made on the server that the message arrives, the email can be received, rejected, checked further by other applications running on the server or arrive to the recipient to be checked by the checking applications installed on his computer.

SPF record Syntax

The SPF record is a TXT DNS record that's added to a domain's zone file. Each domain must have only one SPF record. For example, such a record has the following syntax:

v=spf1 a a:webtool.gr mx ip4:192.168.1.1 ip6:2001:0C8:E004:0001:0000:0000:0000:F00A include:webnew.gr -all

Each SPF record necessarily starts with the version number which is: “v=spf1”.