What is an SPF record?
An SPF record is a DNS record whereby you can verify the sender of an email. SPF records are mainly used in large websites who send large numbers of emails, such as confirmation emails of online orders or webmail services, for instance.
When sending an email, the sending domain's DNS server checks whether the IP address of the sending mail server has been authorized to actually send emails on behalf of that domain name. This way, spam can be filtered and a closed circle is created in which the email can be sent.
Emails that are not sent on behalf of the IP address of the SPF record can be regarded as spam by the receiving mail server.