The SPF (Sender Policy Framework, formerly also Sender Permitted From) is a spam protection method used for sender authentication. In the DNS records of a domain additional information in the form of SPF records are stored. These additional SPF entries in the DNS contain detailed information about the sending mail servers.
The receiving mail server has the possibility via the SPF record of the domain to check whether the received e-mail comes from an authorized mail server or from an unauthorized server. In the latter case, the email can be identified via the SPF spam protection and declared as SPAM.
If an e-mail is sent to the receiving mail
server, it checks which server the
transmitted message was sent from.
In the DNS settings of the sending domain,
all servers that are authorized to send
e-mails can be configured with the help
of an SPF-record.
If the details of the SPF-record match they
sender information of the e-mail, the e-mail
will be delivered. Otherwise it will be treated as SPAM.