AD Connect - sync AD information and not Exchange info - using CodeTwo Migration tool

I want to use AD Connect only to sync AD information and not Exchange info for I'm migrating on premise Exchange to Office 365, however, I'm using a 3rd party tool to migrate.. This being CodeTwo Office 365 migration..  So.. Here's where I'm at..  AD Connect synced users to Office 365 Online Exchange, however, the mailbox isn't created yet for it assumed I'm migrating via AD connect and not my 3rd party tool.. So.. On the user details page I get the below message.  I found a few articles stating to not sync the ExchangeGUID, however, the accounts are already synced.  So.. What should I do?  

This user's on-premises mailbox hasn't been migrated to Exchange Online. The Exchange Online mailbox will be available after migration is completed.
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Sajid Shaik MSystem AdminCommented:
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Adam BrownSr Solutions ArchitectCommented:
AD Connect isn't a migration tool. It's a Directory Sync tool that copies attributes from Onprem DCs to Azure AD. This allows you to have Single Sign On, password sync, and other great features. Not really sure why CodeTwo has issues when you sync the msexchmailboxguid attribute, but whatevs. Sajid's link gives specifics on how to block that from happening. Note, though, that it requires you to delete all existing users for it to work.

That said, onprem Exchange to O365 migrations are usually best handled with the migration tools available in O365. Third party tools add cost and complexity that is rarely justified, because they don't significantly improve migration speed or ease.
stop AD connect synchronization schedules
Set-ADSyncScheduler -SyncCycleEnabled $false

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Then delete all already synced objects in cloud forcefully by running below command
Get-Msoluser -All | remove-Msoluser -Force
Get-Msoluser -All | remove-Msoluser -RemovefromRecycleBin -Confirm:False

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change AD sync configuration to exclude exchangeguid attribute from Azure AD Connect and resync AD connect

Also note that with this attribute removed, you won't be able to do reverse migration in case if required with MS native tools, check with 3d party vendor if he can provide that functionality as well
Agree with Adam Brown,
Microsoft provides you a detailed, excellent guidance.
The most important resources are:
1. Microsoft Deployment Assistant.
2. Ways to migrate to Office365.
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