Note: This page serves as an introduction and quick overview of SPF mechanism syntax. For the complete and definitive picture, please see the specification.
Domains that do not send emails can still be used in email spoofing or phishing attacks, but there are specific types of DNS text (TXT) records that can be used to stifle attackers. Each of these records sets rules for how unauthorized emails should be treated by mail servers, making it harder for attackers to exploit these domains.
SPF "breaks" email forwarding. SRS is a way to fix it. SRS is a simple way for forwarding MTAs to rewrite the sender address.
For a mail transfer agent (MTA), the Sender Rewriting Scheme (SRS) is a scheme for rewriting the envelope sender address of an email message, in view of remailing it. In this context, remailing is a kind of email forwarding. SRS was devised in order to forward email without breaking the Sender Policy Framework (SPF)
In my previous post Custom Domain E-mails With Postfix And Gmail: The Missing Tutorial, we set up a Postfix mail server on a custom domain that integrates seamlessly with Gmail.
However, the tutorial skipped two important security standards that will help prevent e-mails routed through our server from being marked as spam: DKIM and SRS. This article will show you how to add support for DKIM and SRS to a Postfix server. //
DKIM, short for DomainKeys Identified Mail, is a mechanism for
- A sender e-mail program to sign an outgoing e-mail message, and
- A recipient e-mail program to verify said signature.
SRS, short for Sender Rewriting Scheme, is a standard for including forwarding / relay information in a forwarded / relayed e-mail message.
All of your MX record, DNS, blacklist and SMTP diagnostics in one integrated tool. Input a domain name or IP Address or Host Name. Links in the results will guide you to other relevant tools and information. And you'll have a chronological history of your results.
If you already know exactly what you want, you can force a particular test or lookup. Try some of these examples:
SPF Record Syntax
Domains define zero or more mechanisms. Mechanisms can be used to describe the set of hosts which are designated outbound mailers for the domain.
The guidelines in this article can help you successfully send and deliver email to personal Gmail accounts. Starting in 2024, email senders must meet the requirements described here to send email to Gmail personal accounts. A personal Gmail account is an account that ends in @gmail.com or @googlemail.com.
For the latest updates about sender requirements, visit the Email sender guidelines FAQ. //
When increasing sending volume, keep in mind:
- Increasing the sending volume too quickly can result in delivery problems. As you gradually increase your sending email volume, use Postmaster Tools to monitor email delivery.
SPF helps prevent your outgoing email from being marked as spam by receiving email servers. Set up SPF by adding an SPF DNS TXT record (SPF record) to your domain.
An SPF record is a line of text that you add to your domain, following your domain provider’s instructions. The line of text uses special syntax and lists all the servers that send email for your domain. Here’s an example SPF record:
v=spf1 include:_spf.google.com ~all
When receiving servers get email messages from your domain, they check the SPF record to verify that the messages came from authorized servers.
DMARC tells receiving email servers what action to take on messages from you that don't pass SPF or DKIM authentication. The action options are reject, quarantine, or deliver the message. You can also get reports that help you identify possible authentication issues and malicious activity for messages sent from your domain. Set up DMARC by adding a DMARC DNS TXT record (DMARC record) to your domain.
Important: Starting February 2024, Gmail requires the following for senders who send 5,000 or more messages a day to Gmail accounts: Authenticate outgoing email, avoid sending unwanted or unsolicited email, and make it easy for recipients to unsubscribe. Learn more about requirements for sending 5,000 or more emails per day.
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