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.
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:
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.