Entra Connect synchronizes on-prem accounts to Microsoft 365. This means when the two synchronizes, on-prem accounts will be created in Microsoft 365. If there are on-prem accounts and Microsoft 365 accounts beforehand that are not synchronized, this can cause issues. To resolve the issue, go onto AD DS and select attribute editor for these accounts. Go to proxyAddress and write “SMTP:<Email address of Microsoft 365 account>”. This will synchronize the appropriate two separate accounts.
Log into the admin portal of Microsoft 365 and got to Identity. Under Entra ID, select Entra Connect. Select Manage and download connect sync agent
Run Azure Ad Connect. Customize settings and select Install with nothing selected.
At User sign-in select Password Hash Synchronization.
Enter Global Administrator M365 Credentials
Click add directory
Create a new AD account and input an enterprise admin account
Select Next
Select Continue without matching all UPN suffixes to verified domains. Click Next
Click Next
Synchronize all users and devices. Click Next
Click Next
Install