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 6.0.0 or later
Issue: Mailbox not found for this user error.
Resolution: Typically Active Directory User account and his remote mailbox are linked by UserPrincipalName (UPN) attribute. So, when a remote mailbox not found, the most typical root cause is that Active Directory user UPN does not match the corresponding Office 365 account UPN.
You should correct the user UPNs so that they become the same in Active Directory and Office 365.