Solved: Outlook Legacy for Mac and Apple Mail Could Not Add Microsoft 365 Accounts

Problem

We encountered an issue where Microsoft 365 email accounts could not be added using:

• Outlook Legacy for Mac
• Apple Mail
• macOS Internet Accounts

The issue affected:

• Multiple Microsoft 365 users
• Multiple Mac devices
• Newly created macOS user profiles

Symptoms

• Outlook for Mac (New Outlook) worked correctly.
• Outlook on the Web (OWA) worked correctly.
• Outlook Legacy for Mac failed to add the account.
• Apple Mail failed during account setup.
  • macOS Internet Accounts returned:Problem We encountered an issue where Microsoft 365 email accounts could not be added using: Outlook Legacy for MacApple Mail macOS Internet Accounts The issue affected: Multiple Microsoft 365 users Multiple Mac devices Newly created macOS user profiles Symptoms Outlook for Mac (New Outlook) worked correctly.Outlook on the Web (OWA) worked correctly.Outlook Legacy for Mac failed to add the account.Apple Mail failed during account setup.macOS Internet Accounts returned: The operation couldn't be completed (com.apple.accounts error 3)

Root Cause

The issue was caused by Exchange Web Services (EWS) being disabled at the organizational level but not in the account.

Verification: EwsEnabled : False

    Get-OrganizationConfig | Select EwsEnabled

Result:

    EwsEnabled : False

Solution

Enable EWS organization-wide:

      Set-OrganizationConfig -EwsEnabled $true