Troubleshooting Mailbox not found for this user error

Summary: When you open the properties of an Active Directory user remote mailbox, you may see the error: Mailbox not found for this user.  This article explains how to resolve this error.

Applies to: Cayosoft Administrator 9.0.0 or later

ID: KB20191022-1

Issue: Mailbox not found for this user error.

Resolution: 

1. Typically Active Directory User account and his remote mailbox are linked by UserPrincipalName (UPN) attribute. So, when a remote mailbox is not found, the typical root cause is that the Active Directory user UPN does not match the corresponding Office 365 account UPN.
   You should correct the user UPNs to become the same in Active Directory and Office 365.
   
2. Check that the ObjectId value in the msDS-ExternalDirectoryObjectId attribute in on-premise Active Directory matches the ObjectId in the Azure Active Directory.