In the world of email security, DKIM (DomainKeys Identified Mail) stands as a crucial line of defense against spoofing and phishing attacks. When used in conjunction with SPF (Sender Policy Framework), DKIM ensures that your domain remains secure and trustworthy. But what exactly is DKIM, and how does it work? Let’s dive in.
What is DKIM?
DKIM is an advanced security feature designed to authenticate the legitimacy of emails sent from your domain. When DKIM is enabled, every email sent from your server is digitally signed using cryptographic authentication. This digital signature allows the receiving server to verify the authenticity of the email.
Here’s how it works: DKIM uses a private key to encrypt the header of all outgoing mail. The receiving server then looks for the DKIM public key, which is published in the DNS of the sending domain, to decode the signature. If the email comes from an unauthorized server, the signature cannot be decoded, effectively preventing any spoofing attempts.
How Does DMARC Work with DKIM?
DMARC (Domain-based Message Authentication, Reporting, and Conformance) builds on the foundations laid by DKIM and SPF. When DKIM is enabled, all outgoing emails carry an embedded DKIM encryption key or public key. This encryption ensures that any tampering during transit can be detected.
Upon receiving the email, the recipient server sends a validation request to the sender’s domain to verify the public key against the private key stored in the sender’s DNS record. If the private key can decode the public key, the email is deemed legitimate. If not, it’s flagged as SPAM.
Why DKIM is Essential After SPF
While SPF is effective, it has its limitations, especially when it comes to email forwarding. Changes in the connecting IP during forwarding can cause SPF checks to fail, leading to legitimate emails being marked as SPAM.
This is where DKIM comes into play. By working together, SPF and DKIM provide a robust security framework. If an email fails the SPF check, the DKIM verification process ensures that the email can still be validated. Successful DKIM validation means the email is legitimate, thus ensuring safe delivery.
How to Create and Publish DKIM Records
To implement DKIM for your Office 365 custom domain, you need to publish two CNAME records in your DNS. Office 365 uses these records to perform automatic key rotations, enhancing security.
Here’s a step-by-step guide to creating and publishing DKIM records:
- Publish Two CNAME Records in DNS
- For each custom domain in addition to the initial domain in Office 365, publish two CNAME records:
- Host name: selector1._domainkey Points to address or value: selector1-DOMAIN-com._domainkey.DOMAIN.onmicrosoft.com TTL: 3600
- Host name: selector2._domainkey Points to address or value: selector2-domain-com._domainkey.domain.onmicrosoft.com TTL: 3600
- For each custom domain in addition to the initial domain in Office 365, publish two CNAME records:
- Enable DKIM Signing in the Office 365 Admin Center
- Sign in to Office 365 with your work or school account.
- Select the app launcher icon in the upper-left and choose Admin.
- In the lower-left navigation, expand Admin and choose Exchange.
- Go to Protection > DKIM.
- Select the domain for which you want to enable DKIM and choose “Enable” for “Sign messages for this domain with DKIM signatures.” Repeat this step for each custom domain.
By following these steps, you ensure that your emails are not only delivered securely but also maintain their legitimacy, thereby protecting your domain from potential security threats.
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HARISH KUMAR
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