A case came in the other day where a customer was unsure of what syntax to use when communicating with Exchange 2010.
When you load up a 'Provision user in Exchange' action in Nintex Workflow Designer, the mailbox container has an option to browse to the Database via an LDAP Picker control:
If you are using Exchange 2003, using the LDAP picker is perfectly fine. If you are using Exchange 2007/2010/2013 you will run into issues with locating the target Mailbox Database.
Instead of using the values the LDAP picker populates, consider using the browser to only retrieve the name of the database and populate the 'Mailbox container' field with this value:
If this action is not configured accordingly you will likely see error messages in your ULS logs that are similar to this:
Category: (Legacy) Workflow Infrastructure
System.ApplicationException: Provisioning user on Exchange 2010 failed. Check the event logs on the Exchange 2010 server to determine the cause. at Nintex.Workflow.Activities.ProvisionExchangeUserEmailActivity.ProvisionExchangeUserEmail(NWWorkflowContext ctx) at Nintex.Workflow.Activities.ProvisionExchangeUserEmailActivity.Execute(ActivityExecutionContext executionContext) at System.Workflow.ComponentModel.ActivityExecutor`1.Execute(T activity, ActivityExecutionContext executionContext) at System.Workflow.ComponentModel.ActivityExecutorOperation.Run(IWorkflowCoreRuntime workflowCoreRuntime) at System.Workflow.Runtime.Scheduler.Run()
Additionally, the workflow will fail to complete.