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Once your domain is added, follow the steps as shown below to configure DKIM. If you do not see it, add your accepted domain from domains page. Steps to Create, enable and disable DKIM from Microsoft Defender portalĪll the accepted domains of your tenant will be shown in the Microsoft Defender portal under the DKIM page. If the message is verified, the DKIM check passes. The verifying domain, or recipient's domain, then uses the d= field to look up the public key from DNS, and authenticate the message. The signing domain, or outbound domain, is inserted as the value of the d= field in the header. We recommend using both SPF and DKIM, as well as DMARC in your deployment.ĭKIM uses a private key to insert an encrypted signature into the message headers. Because DKIM relies on public key cryptography to authenticate and not just IP addresses, DKIM is considered a much stronger form of authentication than SPF. The addition of DKIM in this scenario reduces false positive spam reporting.

In this example, if you had only published an SPF TXT record for your domain, the recipient's mail server could have marked your email as spam and generated a false positive result. Since the digital signature stays with the email message because it's part of the email header, DKIM works even when a message has been forwarded as shown in the following example. When you forward a message, portions of that message's envelope can be stripped away by the forwarding server. SPF adds information to a message envelope but DKIM encrypts a signature within the message header.

How DKIM works better than SPF alone to prevent malicious spoofing You want to set up DKIM keys for email originating out of a third-party domain, for example, if you use a third-party bulk mailer.You want to customize your CNAME records.You're going to set up DMARC too ( recommended).You have more than one custom domain in Microsoft 365.However, you should manually configure DKIM for your custom domain in the following circumstances: Microsoft-365's built-in DKIM configuration is sufficient coverage for most customers. If you don't set up DKIM for your custom domain, Microsoft 365 creates a private and public key pair, enables DKIM signing, and then configures the Microsoft 365 default policy for your custom domain. You can choose to do nothing about DKIM for your custom domain too.

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DKIM verification helps the receiving servers confirm the mail is really coming from your domain and not someone spoofing your domain. The public key is published in the domain's DNS records, and receiving servers can use that key to decode the signature. In basic, a private key encrypts the header in a domain's outgoing email. Email systems that get email from your domain can use this digital signature to help verify whether incoming email is legitimate. When you configure DKIM, you authorize your domain to associate, or sign, its name to an email message using cryptographic authentication. For more information about domains, see Domains FAQ.ĭKIM is one of the trio of Authentication methods (SPF, DKIM and DMARC) that help prevent attackers from sending messages that look like they come from your domain.ĭKIM lets you add a digital signature to outbound email messages in the message header. That means you don't need to do anything to set up DKIM for any initial domain names (for example, ). Microsoft 365 automatically sets up DKIM for its initial '' domains.

Next steps: After you set up DKIM for Microsoft 365.

Set up DKIM so that a third-party service can send, or spoof, email on behalf of your custom domain.

Default behavior for DKIM and Microsoft 365.

Disabling the DKIM signing policy for a custom domain.

Steps to configure DKIM for more than one custom domain.

Error: No DKIM keys saved for this domain.

Steps to manually set up DKIM using PowerShell.

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Steps to manually upgrade your 1024-bit keys to 2048-bit DKIM encryption keys.

Steps to Create, enable and disable DKIM from Microsoft Defender portal.

How DKIM works better than SPF alone to prevent malicious spoofing.

This article lists the steps to use DomainKeys Identified Mail (DKIM) with Microsoft 365 to ensure that destination email systems trust messages sent outbound from your custom domain.

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Learn about who can sign up and trial terms here. Did you know you can try the features in Microsoft Defender XDR for Office 365 Plan 2 for free? Use the 90-day Defender for Office 365 trial at the Microsoft Defender portal trials hub.

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