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What Is SPF Check?

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Last updated March 28th, 2013 by Boyana Peeva in Explainer

EmailSPF (Sender Policy Framework), is a system that authenticates and identifies servers that your domain can use to send mail. The aim is to ensure that unauthorized spammers and cyber criminals do not send messages to recipients that supposedly come from your domain. With SPF in place, recipients can check the available records to determine whether the received e-mails originated from an authorized mail server. Keep reading to learn more about the sender policy framework.

SPF Versus Sender ID

Contrary to popular belief, SPF and sender ID is quite different. The confusion stems from the fact that both use the same policy records syntax, validate e-mail sender addresses, and publish policy records in DNS. However, this is where the similarity ends. SPF validates two parts of the e-mail sender's address: the MAIL FROM address and the HELO domain. You can find this information by checking the records published by domain owners. It is important to note that both the HELO domain and the MAIL FROM are part of the SMTP protocol. On the other hand, sender ID is a Microsoft protocol that validates a single field of the e-mail address header. The header to validate depends on the choice made by the Purported Responsible Address (PRA) algorithm.

How SPF works

To validate messages, the sender policy framework compares the sender's mail servers to a list of authorized IP addresses already in the DNS record. The sender receives a rejection message if the comparison process does not give a positive result. If the comparison is successful, the server inserts the Return-Path field in the message. The good news is that domains that use SPF are not easy to compromise. In addition, messages originating from domains that use SPF will likely get through to recipients. This is because most e-mail filters do not block messages from SPF-protected domains.

SPF Best Practices

Some of the steps that you can use to ensure SPF best practices include:

- Updates

Like any other technology, it is wise to use the latest SPF implementations. For example, ensure you use a program supporting RFC 4408 processing limits.

- Web-Generated e-mailers

If you use web-generated e-mailers, you risk your e-mail messages appearing as spam. This is because most sites that send web-generated e-mails do not form the list contained in the domain owner's SPF records. To ensure this does not happen, set up your e-mail headers correctly. The rule of thumb is to use your domain as part of the "MAIL FROM" address. You can then add the "Reply-To" or the "Sender" header.

- Use Other E-mail Validation Technologies

Relying on one e-mail authentication protocol or technology is not a good idea. Instead, it would be best if you used other technologies to authenticate messages as well. For example, you can use technologies such as DMARC and DKIM together with SPF. This will make it harder for cyber criminals to forge your domain name and send spam messages.

Mistakes to avoid

When creating your SPF records, it is easy to make mistakes. To avoid making mistakes, start by listing all your domains if you currently have more than one domain. This prevents hackers from using domains that you have not listed in the SPF records to send spam. Secondly, only list servers that send mail to web users. There is no need to list servers that receive mail from web users. Thirdly, never list your servers more than once. This is because using multiple host names only complicates DNS lookups. Other mistakes you must avoid include testing any new SPF record, using the correct DNS server to publish your SPF record, and using "MX" with your domain names.

Authenticating messages that originate from domain names is very important. SPF ensures that hackers and spammers do not use your domains to send spam. In addition, it reduces the risk of authentic e-mail messages ending up in the spam folder.

Boyana Peeva

Believes that the glass is rather half-full and that nothing is bigger than the little things. Enjoys writing, reading, and sharing content – information is power.

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