What is SPF?

A: SPF stands for Sender Policy Framework, an email authentication protocol that allows domain owners to specify the servers authorized to send emails on behalf of their domains.

Q: How does SPF work?

A: When an email is sent from your domain, the receiving email server checks your DNS for an SPF record. This record contains a list of all IP addresses that are authorized to send email from your domain. If the sender’s IP address matches one of the addresses in the SPF record, the email is authenticated.

Q: What is the SPF record?

A: The SPF record is a TXT record on your DNS that contains the details of your domain's authorized sending servers. It is crucial to implement SPF on your domain.

Q: What is included in an SPF record?

A: An SPF record consists of a version, mechanisms, qualifiers, and modifiers. The version indicates the version of SPF being used, while mechanisms are the elements that direct the receiving server to check specific records on DNS or use certain protocols when performing SPF authentication. Qualifiers indicate whether the mechanism passes, fails, or soft fails, and modifiers are optional and can be used to redirect or explain the SPF record.

Q: What are some examples of SPF mechanisms?

A: There are several SPF mechanisms, including:

  • "a" - All the A records of the domain are tested.
  • "mx" - MX records specify which servers should be used to relay emails.
  • "ip4" - Specifies an IPv4 network range for the sender's IP address.
  • "ip6" - Specifies an IPv6 network range for the sender's IP address.
  • "ptr" - The hostname for the sender's IP is looked up using PTR queries.

Q: What are some examples of SPF qualifiers?

A: Qualifiers are used to indicate whether the mechanism passes, fails, or soft fails. Some examples of SPF qualifiers include:

  • "+" - Pass. The SPF record designates the IP address to be allowed to send.
  • "-" - Fail. The SPF record designates the IP address NOT be allowed to send.
  • "~" - SoftFail. The SPF record designates the IP address NOT be allowed to send, but is in transition.
  • "?" - Neutral. The SPF record designates that nothing can be said about the validity of the IP address.

Q: What are some SPF record limitations?

A: SPF records have several in-built limitations to reduce processing load on receiving email servers, including:

  • Only one SPF record per domain name is allowed.
  • The SPF record can't have more than 10 mechanisms that result in DNS lookups.
  • There is a limit of 10 MX records that the server can query when analyzing the mx mechanism.
  • There is a limit of 10 PTR queries that the server can perform when analyzing the ptr mechanism.