On a Windows computer, open Powershell:

Install ExchangeOnlineManagement

Install-Module -Name ExchangeOnlineManagement -RequiredVersion 1.0.1

import-module exchangeonlinemanagement

Connect to Exchange online

Connect-ExchangeOnline -UserPrincipalName admin@yourdomain.onmicrosoft.com -ShowProgress @true

Create a key:

New-DkimSigningConfig -DomainName your.domain.com -KeySize 2048 -Enabled $True

WARNING: The config was created but can’t be enabled because the CNAME records aren’t published. Publish the following two
CNAME records, and then enable the config by using Set-DkimSigningConfig.
selector1-yourdomain-com-au._domainkey.yourdomain.onmicrosoft.com
selector2-yourdomain-com-au._domainkey.yourdomain.onmicrosoft.com

 

Logon your DNS hosting portal, add below two records:

  • Type: cname
  • name: selector1._domainkey
  • value: selector1-yourdomain-com-au._domainkey.yourdomain.onmicrosoft.com
  • TTL: 1 hour

 

Wait for about 15 minutes, then issue the below command:

Set-DkimSigningConfig -Identity charlden.com.au -Enabled $true

Now if you logon the Exchange Admin Center > protection > dkim , you will find below:

 

 

To find a detailed info about this key:

 

Get-DkimSigningConfig -Identity charlden.com.au | fl