Easy! IT | Security | Sender Policy Framework

This article is a rough explanation of the Sender Policy Framework.

Everything might be not exactly correct in this article but it’s very useful for beginners to understand IT terms. If you want to learn IT but you don’t have any experience to work in the IT industry, I wish it helps you to understand IT. And I hope that this article motivates you to study IT more.

Let’s start our 3 minutes lesson!

What is the Sender Policy Framework?

SPF stands for Sender Policy Framework.
SPF is an email authentication method to check who sends the email.
SPF helps to prevent your mail users from receiving spam mails.

1. Email service

You can send messages with a digital letter called an email. Users can send an email with a client (mail application such as Gmail, yahoo mail, outlook and so on), and mail servers receive and deliver them.

In short, an email is a letter in a computing world, and the mail server is a post office in that world.

**A user sends messages with an email client, and a mail server is a post office.**

2. Why You Need SFP

SMTP is a very nice guy.

What is SMTP?: Easy! IT | Protocol | Simple Mail Transfer Protocol | Japan Teams

SMTP is well-known as a super nice guy, which all emails are welcome to and sends them. But hackers always look for kindness(weakness). They send emails pretending to be someone. Then people need some measures to prevent hackers from sending mails as the different people. SPF is developed as the solution, which is the way to link an email to a domain.

What SPF action is:

The domain owner publishes the list of allowed senders.
Email receivers check the list to if a sender is allowed.
If so, the link between the domain and the email is established.

What is DNS?: IT Learning | Network | DNS | Japan Teams

**A mail server asks a DNS server before it sends emails with SMTP.**

**Caching DNS asks Authoritative DNS if there is not the domain on the list.**

More details:Publishing a policy

1. Publishing a policy

A domain administrator adds additional records to their exiting DNS to identify the machines authorized to send an email. That record is called an SPF record. The record contains IP addresses that are verified to send emails on behalf of their domains.

2. Lookup SPF record

When a mail server receives an email via SMTP, a mail server asks an SPF record to the DNS server which MAIL FROM command specifies.

3.Caching DNS checks the SPF record

Caching DNS server asks for a content DNS(Authoritative DNS) server if it doesn’t cache the SPF record.

4. Comparing IP addresses

After receiving the SPF record from an authoritative server, a caching DNS server answers the SPF record to a mail server that receives the email. Then, a mail server compares the IP address from the SPF record with the IP address of the mail server that sent the email. If IP addresses match, an SPF verify succeeds. If those IP addresses are different, an SPF verify fails and the mail server rejects the mail.