- 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.
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?
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
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.
