Knowledgebase

For each domain for which you want to add a DKIM signature in DNS, you need to publish two CNAME records.

For Office 365, the selectors will always be to selector CNAMES "selector1" and "selector2".  

• domainGUID is the same as the domainGUID in the customized MX record for your custom domain that appears before mail.protection.outlook.com. For example, in the following MX record for the domain contoso.com, the domainGUID is contoso-com:

  Copy

  contoso.com.  3600  IN  MX   5 contoso-com.mail.protection.outlook.com
  

• initialDomain is the domain that you used when you signed up for Office 365. Initial domains always end in onmicrosoft.com. For information about determining your initial domain, see Domains FAQ.

For example, if you have an initial domain of cohovineyardandwinery.onmicrosoft.com, and two custom domains cohovineyard.com and cohowinery.com, you would need to set up two CNAME records for each additional domain, for a total of four CNAME records.

Host name:			selector1._domainkey
Points to address or value:	**selector1-cohovineyard-com**._domainkey.cohovineyardandwinery.onmicrosoft.com
TTL:				3600

Host name:			selector2._domainkey
Points to address or value:	**selector2-cohovineyard-com**._domainkey.cohovineyardandwinery.onmicrosoft.com
TTL:				3600

Host name:			selector1._domainkey
Points to address or value:	**selector1-cohowinery-com**._domainkey.cohovineyardandwinery.onmicrosoft.com 
TTL:				3600
 
Host name:			selector2._domainkey
Points to address or value:	**selector2-cohowinery-com**._domainkey.cohovineyardandwinery.onmicrosoft.com 
TTL:				3600

To enable DKIM signing for your custom domain through the Office 365 admin center

1. Sign in to Office 365 with your work or school account.

2. Select the app launcher icon in the upper-left and choose Admin.

3. In the lower-left navigation, expand Admin and choose Exchange.

4. Go to Protection > dkim.

5. Select the domain for which you want to enable DKIM and then, for Sign messages for this domain with DKIM signatures, choose Enable. Repeat this step for each custom domain.

For more information view Microsofts article Use DKIM to validate outbound email sent from your custom domain in Office 365 at https://docs.microsoft.com/en-us/office365/SecurityCompliance/use-dkim-to-validate-outbound-email