When attempting to provision an Exchange mailbox the following error is seen:
"  Error executing projection step (Mailbox) of projection configuration (Provisioning (Provisioning)).
 Error executing synchronization step (Mailbox)!
 Method (Insert (Insert)) could not be executed successfully.
[System.Management.Automation.ActionPreferenceStopException] The running command stopped because the preference variable "ErrorActionPreference" or common parameter is set to Stop: The Mailbox database "Microsoft.Exchange.Provisioning.LoadBalancing.MailboxDatabaseWithLocationInfo" isn't on a server running Exchange 2013 or a later version. If you want to create or enable a Exchange 2010 mailbox, or want to enable the archive or remote archive for a Exchange 2010 Sp1 mailbox, please execute the cmdlet from a Exchange 2010 server."
This error comes from Microsoft Exchange, not One Identity Manager. Exchange can only create objects that are of the same version as the version of Exchange being used. So Exchange 2016 is not able to create Exchange 2010 objects. Attempting to use Identity Manager in a mixed version Exchange environment will produce errors for this reason.
Please see the following links for more information: