DKIM uses a pair of keys, one private and one public, to verify messages. A private domain key adds an encrypted signature header to all outgoing messages sent from your Gmail domain. A matching public key is added to the Domain Name System (DNS) record for your Gmail domain. Email servers that get messages from your domain use the public key to decrypt the message signature and verify the signed message sources.

What if my domain already has a DKIM key?

If you already use DKIM in your domain (with another email system), you must generate a new, unique domain key to use with Gmail. Domain keys include a text string called the selector prefix, which you can modify when you generate the key. The default selector prefix for the Google Workspace domain key is google. When you generate the key, you can change the default selector prefix from google to the text of your choice, and use the new selector in parallel with the domain's existing DKIM key configuration.

How do I set up DKIM for a server that modifies the content of outgoing emails?

If you use an outbound mail gateway that changes outgoing messages, the DKIM signature is voided. One example is email servers that add a footer to every outgoing message. To avoid this issue, take one of these actions.

What is DKIM and DMARC?

DKIM, SPF and DMARC are all email verification technologies that are free for your organization. DKIM stands for DomainKeys Identified Mail, an email confirmation method. Method This is another way to link an email to a domain.

What happens when DKIM fails?

Migomail When DKIM alignment fails—or when the d= value in the From header does not match the d= value in the DKIM signature—it can negatively affect delivery efficiency as mailbox providers may send messages to the Spam folder. Or block it completely.

What is DKIM alignment?

DKIM alignment occurs when the parent domain of your email's DKIM signing domain matches the header domain. The two types of DKIM alignment are relaxed alignment and strict alignment. If you do not specify strict alignment, relaxed alignment is assumed.

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Understanding DKIM

DomainKeys Identified Mail, or DKIM, is a technical standard that helps protect email senders and recipients from spam, spoofing, and phishing. It is a form of email authentication that allows an organization to claim responsibility for a message in a way that can be validated by the recipient.

Specifically, it uses an approach called “public key cryptography” to verify that an email message was sent from an authorized mail server, in order to detect forgery and to prevent delivery of harmful email like spam. It supplements SMTP, the basic protocol used to send email, because it does not itself include any authentication mechanisms.

How does it work?

It works by adding a digital signature to the headers of an email message. That signature can be validated against a public cryptographic key in the organization’s Domain Name System (DNS) records. In general terms, the process works like this:

A domain owner publishes a cryptographic public key as a specially-formatted TXT record in the domain’s overall DNS records.

When a mail message is sent by an outbound mail server, the server generates and attaches a unique DKIM signature header to the message. This header includes two cryptographic hashes, one of specified headers, and one of the message body (or part of it). The header contains information about how the signature was generated.

When an inbound mail server receives an incoming email, it looks up the sender’s public DKIM key in DNS. The inbound server uses this key to decrypt the signature and compare it against a freshly computed version. If the two values match, the message can be proved to authentic and unaltered in transit.

What is a DKIM signature?

A DKIM signature is a header added to email messages. The header contains values that allow a receiving mail server to validate the email message by looking up a sender’s DKIM key and using it to verify the encrypted signature. It looks something like this:

A DKIM signature header packs in a lot of information, as it is intended for automated processing. As you can see in this example, the header contains a list of tag=value parts. Notable tags include “d=” for the signing domain, “b=” for the actual digital signature, and “bh=” for a hash that can be verified by recalculating using the sender’s public key.

Signatures are by definition unique from message to message, but these basic elements will be present in every DKIM signature header.

How is it related to SPF, DMARC, or other standards?

DKIM, SPF, and DMARC are all standards that enable different aspects of email authentication. They address complementary issues.

SPF allows senders to define which IP addresses are allowed to send mail for a particular domain. DKIM provides an encryption key and digital signature that verifies that an email message was not faked or altered. DMARC unifies the SPF and DKIM authentication mechanisms into a common framework and allows domain owners to declare how they would like email from that domain to be handled if it fails an authorization test.

Do I need DKIM?

If you are a business sending commercial or transactional email, you definitely need to implement one or more forms of email authentication to verify that an email is actually from you or your business. Properly configuring email authentication standards is one of the most important steps you can take to improve your deliverability. However, by itself it only goes so far; Migomail and other email experts recommend also implementing SPF and DMARC to define a more complete email authentication policy.

Does Migomail support it?

Yes. Migomail implements and adheres to email authentication standards including DKIM. In fact, all email we deliver for our users is required to be authenticated. Configuring it is an important step for verifying sending domains when you set up a new Migomail account.

How can I verify my settings?

Migomail's Validator is part of our free email tools for developers. It’s the easiest way to verify your messages have working DKIM signatures.

Learn More about DKIM

Read more about DKIM best practices

Learn more about DKIM with these resources from Migomail’s email experts and elsewhere on the web.

DKIM.org. The group that developed the DKIM standard has published detailed explanations, how-to’s, and news about DKIM. How to Explain DKIM to Your Grandmother [Infographic]. An easy-to-understand explanation of the basic concepts behind DKIM and how it helps to make email safer.

Three DKIM Challenges You Might Not Know About. An email pro offers three practical tips for making sure you’re implementing DKIM the right way to provide maximum protection for your brand integrity as an email sender. Understanding SPF and DKIM In Sixth Grade English. An easy-to-understand explanation of how SPF and DKIM work together to ensure email is authenticated. Get help with DKIM in the Migomail Support Center

Learn more about how to configure and use DKIM with the Migomail service in the Migomail Support Center.

Setting up SPF and DKIM with Domain Providers. How-to’s for configuring records that support email authentication at various DNS hosting providers. Why do we need to configure SPF and DKIM to send anything? A great explanation of why Migomail requires that all the email we deliver be authenticated with standards like SPF or DKIM. Troubleshooting SPF and DKIM Verification. Tips for ensuring DNS records related to email authentication are propagated properly.