Failed to disable the mailbox 2c6758c5-8013-4b9a-b4b3-400901e3124b due to a conflict in directory settings.

 

Scenario

Unable to remove cloud user mailbox which is synced from on premise server,

Error on the Admin Portal when select the user: Exchange: Failed to disable the mailbox 2c6758c5-8013-4b9a-b4b3-400901e3124b due to a conflict in directory settings. To disable this mailbox, first run Enable-RemoteMailbox on-premises. After the next Dirsync sync cycle, run Disable-RemoteMailbox on-premises to disable this mailbox in the datacenter.

The Fix
Example: I am using “Karif Geneva” as my problematic user.
You can check the Routing E-mail Address using the EMC for another user and make sure it's domain is correct. Check below,

Enable Remote user Mailbox
Enable-RemoteMailbox karifg@yourdomain.com -PrimarySmtpAddress karifg@yourdomain.com –RemoteRoutingAddress karifg@tenant.onmicrosoft.com

Add additional email alias to users
Set-RemoteMailbox -Identity karifg@yourdomain.com -EmailAddresses @{add='karifg@service.yourdomain.com'}

Disable user mailbox now
Disable-RemoteMailbox karifg@yourdomain.com

Logon to EMC or Online portal and check whether the user mailbox is removed.

Thanks
@Roshan