In the Office 365 Admin Center, under Users > Active Users, you can see a user called imserviceuser, with no licenses assigned. Under display name, you will see "User account used for integration with third-party services", and the Username will be email@example.com. Status will say Unlicensed.
This user is used for syncing Active Directory objects between Office 365 and Intermedia. It cannot be renamed, hidden, or deleted.