About SPF records

An SPF record defines the mail servers and domains that are allowed to send email on behalf of your domain. Each domain can have one SPF record, but the record can specify additional servers and third parties that are allowed to send email from your domain.

 

• Receiving servers check your SPF record to verify that incoming messages appearing to be from your organization are sent from servers authorized by you.
• The SPF record also tells receiving servers what to do with messages after they're checked.

SPF record format

An SPF record is a line of plain text that includes a list of tags and values. The tags are called mechanisms. The values are typically IP addresses and domain names.

An SPF record is added to your domain provider in the form of a DNS TXT record. Learn more About TXT records.

SPF records can have up to 255 characters. The TXT record file size should be no larger than 512 bytes.

Understand IP addresses

An IP address is used to identify devices and connect to the internet. IP addresses let devices like computers, mobile devices, and servers communicate with each other. Servers that send and receive email are identified by their unique IP address. The SPF record for your domain might need the IP addresses for servers that send email for your domain.

• IP version 4 (IPv4) addresses look like this: 203.0.113.42
• IP version 6 (IPv6) addresses look like this: 2001:db8:14:5:1:2:bf35:2610

IP addresses are typically assigned to networks in blocks. An IP address with a slash (/) indicates a block of IP addresses:

• IPv4: 192.0.2.0/24
• IPv6: 2001:db8:1234::/48

When you use an IP block address in your SPF record, the SPF record is applied to all IP addresses in the block.

SPF record mechanisms

Use the mechanisms in this table to create your SPF record. Receiving mail servers check messages against mechanisms in the order they are listed in the SPF record.

Keep in mind:

• You can use optional SPF record qualifiers (later on this page) with mechanisms. 
• Your TXT record for SPF shouldn’t include more than 10 references to other domains or servers.  These references are called lookups. Learn more in Check the DNS lookups in your SPF record.

Mechanism	Description and values
v	(Required) This is the SPF version. This tag must be the first tag in the record. This mechanism must be: v=spf1.
ip4	Authorizes mail servers by IPv4 address or address range. This value must be an IPv4 address or range in standard format, for example: ip4:192.168.0.1 or ip4:192.0.2.0/24.
ip6	Authorizes mail servers by IPv6 address or address range. This value must be an IPv6 address or range in standard format, for example: ip6:3FFE:0000:0000:0001:0200:F8FF:FE75:50DF or ip6:2001:db8:1234::/48.
a	Authorizes mail servers by domain name, for example: a:example.com
mx	Authorizes one or more mail servers by domain MX record, for example: mx:mail.example.com. If this mechanism isn't in your SPF record, the default value is the MX records of the domain where the SPF record is used.
include	Authorizes third-party email senders by domain, for example: include:servers.mail.net.
all	Specifies that all incoming messages match. We recommend you always include this mechanism in your SPF record. This must be the last mechanism in the SPF record. Any mechanism that comes after the all mechanism in an SPF record is ignored. Should I use ~all or -all? When an SPF record includes ~all (soft fail qualifier), receiving servers typically accept messages from senders that aren't in your SPF record, but mark them as suspicious. When an SPF record includes -all (fail qualifier), receiving servers may reject messages from senders that aren't in your SPF record. If your SPF record isn’t set up correctly, the fail qualifier might cause more messages from your domain to be sent to spam. Tip: To prevent spoofing of domains that don’t send email, use this as the SPF record for the domain: vspf1 ~all.

SPF record qualifiers

A qualifier is an optional prefix you can add to any mechanism in your SPF record. Qualifiers tell the receiving mail server whether to consider a message authenticated when there's a match with a mechanism value, for example:

v=spf1 include:_spf.google.com ~all

In this example, the SPF record authorizes only Google Workspace to send emails for your domain. The all mechanism has a soft fail qualifier ( ~ ), so messages from any senders not in your SPF record fail the SPF check might be sent to spam by the receiving server. If messages from specific senders are consistently sent to spam, make sure those senders are in your SPF record.

 

If you use a hard fail qualifier ( - ) before the all in your SPF record, messages that fail the SPF check are more likely to be rejected by the receiving server, and you can’t use those messages to troubleshoot your SPF record. In this case, Google recommends using DMARC reports to identify all senders for your domain.

Mechanisms are checked in the order they occur in the SPF record. If a mechanism doesn’t have a qualifier and there’s a match, the default action is to pass authentication. When there's no mechanism match, the action default is neutral: the message doesn't pass or fail authentication.

Use these optional qualifiers to tell receiving mail servers how to handle messages that match mechanisms in the SPF record.

Qualifier	Action receiving server takes with a match
+	Passes authentication. The server with matching IP address is authorized to send for your domain. Messages are authenticated. This is the default action when the mechanism doesn’t use a qualifier.
-	Fails authentication. The server with matching IP address is not authorized to send for the domain. The SPF record doesn’t include the sending server IP address or domain so messages won’t pass authentication.
~	Soft fails authentication. It's unlikely that the server with matching IP address is authorized to send for the domain. The receiving server will typically accept the message but mark it as suspicious.
?	Neutral. Neither passes nor fails authentication. The SPF record doesn’t explicitly state that the IP address is authorized to send for the domain. SPF records with neutral results often use ?all.