What is SPF?
Sender Policy Framework (SPF) is a technical standard that protects email senders and recipients from spam; spoofing; and phishing. It is a form of email authentication.
Specifically, it defines a way to validate that an email message was sent from an authorized mail server; in order to detect forgery and to prevent spam. It was designed to supplement SMTP, the basic protocol used to send emails; because SMTP itself does not include any authentication mechanisms.
For example; suppose that your domain; example.com uses Gmail. You create an SPF record that identifies the G Suite mail servers as the authorized mail servers for your domain. When a recipient's mail server receives a message from user@example.com; it can check the SPF record for example.com to determine whether it is a valid message. If the message comes from a server other than the G Suite mail servers listed in the SPF record; the recipient's mail server can reject it as spam.
https://support.google.com/a/answer/33786?hl=en
How it works?
SPF defines the flow of emails coming from legitimate trusted mail server.
- A domain administrator publishes the policy defining mail servers that are authorized to send email from that domain. This policy is called an SPF record; and it is listed as part of the domain’s overall DNS records.
- When an inbound mail server receives an incoming email; it looks up the rules for the bounce (Return-Path) domain in DNS. The inbound server then compares the IP address of the mail sender with the authorized IP addresses defined in the SPF record.
- The receiving mail server then uses the rules specified in sending the domain’s SPF record to decide whether to accept; reject; or otherwise flag the email message.
If your emails land into the junk/spam folder or are checked under fraud detection and rejected then you need to make sure that Maximizer’s SPF record is added into your domain (e.g. GoDaddy account).
Please read more at : https://en.wikipedia.org/wiki/Sender_Policy_Framework