Microsoft 365 automatically sets up DKIM for onmicrosoft.com domains. No steps are needed to use DKIM for any initial domain names (like litware.onmicrosoft.com). For more information about domains, see Domains FAQ. Since both 1024 and 2048 bitness are supported for DKIM keys, these directions will tell you how to upgrade your 1024-bit key to 2048 in Exchange Online PowerShell. Read More