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In the previous article, we had a look at how to configure the SPF record for Office 365. An excellent way to protect both senders and recipients from phishing mail is to configure a DKIM record for Office 365. In this article, we will look at how to configure and enable DKIM record for Office 365.
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What is DomainKeys Identified Mail (DKIM)?
DomainKeys Identified Mail (DKIM) is an authentication process that can help protect both senders and recipients from forged and phishing email. Add DKIM signatures to your domains, so recipients know that email messages actually came from users in your organization and weren’t modified after they were sent.
Check Office 365 DKIM status
Log in to Microsoft 365 admin center. Click under Admin centers on Security.
Click on Threat Management > Policy > DKIM.
Another option is to go straight to the link https://protection.office.com/dkimv2.
Click on the domain in the list view. In this example, the domain exoip.com.
Click on the switch to enable DKIM.
DKIM is by default disabled for every domain you add in Office 365. Microsoft can’t automatically enable this as it relies on certain DNS records added to the domain’s registrar.
A message will show that it can’t enable DKIM because the CNAME record does not exist for this config. That’s correct because we need to add a couple of CNAMES in the domain’s registrar.
Only the message is not showing which two CNAME records we need to add. That’s a bug by Microsoft, and they will hopefully fix this very soon.
Office 365 DKIM records example
An example of how the DKIM records look like for the domain exoip.com:
selector1._domainkey CNAME selector1-exoip-com._domainkey.exoip365.onmicrosoft.com selector2._domainkey CNAME selector2-exoip-com._domainkey.exoip365.onmicrosoft.com
If you want to add more than one domain, change the domain and tenant. Everything else looks the same.
Get Office 365 DKIM selector with PowerShell
Run PowerShell as administrator and Connect to Exchange Online PowerShell.
PS C:\> Connect-ExchangeOnline -UserPrincipalName firstname.lastname@example.org
Run the cmdlet Get-DkimSigningConfig including the domain.
PS C:\> Get-DkimSigningConfig -Identity exoip.com | fl Selector1CNAME,Selector2CNAME Selector1CNAME : selector1-exoip-com._domainkey.exoip365.onmicrosoft.com Selector2CNAME : selector2-exoip-com._domainkey.exoip365.onmicrosoft.com
Add Office 365 DKIM CNAME records to domain’s registrar
Go to the domain’s registrar. Add the two CNAME records.
Pay close attention as some registrars want you to add a dot at the end of the value, and others don’t. You can verify by checking other records and see if they have a dot at the end of their value. If you are not sure, contact your domain’s registrar.
In our example, a dot needs to be added at the end of the value. It will look like below.
Name TTL Type Value ---- --- ---- ----- selector1._domainkey 5 min. CNAME selector1-exoip-com._domainkey.exoip365.onmicrosoft.com. selector2._domainkey 5 min. CNAME selector2-exoip-com._domainkey.exoip365.onmicrosoft.com.
We have to wait 15 minutes to an hour before changes take effect.
Enable Office 365 DKIM
Go back to the Office 365 Security & Compliance Center and Enable DKIM for Office 365.
DKIM record check
Check DKIM record with MxToolbox. Fill in the domain name and selector1. Click DKIM Lookup.
The DKIM selector1 record is published.
Change the lookup field to selector2 and click on DKIM Lookup. The DKIM selector2 record is published.
We did successfully configure the DKIM record for the domain in Office 365.
In the next article, we will change Users UPN with PowerShell.
In this article, you learned how to configure DKIM record for Office 365. Log in to the Microsoft 365 admin portal and go to the DKIM policy. Enabling DKIM for the domain will not work without first creating the CNAME records in the domain’s registrar.
Log in to the domain’s registrar and publish the CNAME records selector1 and selector2. After that, wait for 15 minutes before enabling DKIM in Microsoft 365 admin portal. You can always use MxToolbox to perform a DKIM record test against the domain name and selector for a valid published DKIM key record.
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