Please set the standards based on what is required in your organization. Identify the process of ID creation and any cost attached to it. Now define who should have the official email ID, based on the cost and the requirement. If there are no costs involved, figure out the do's and don'ts for email usage. That should help you determine the allocation better.
Finally, for deletion, there can be only one reason, and that is the end of employment of the employee with the firm. While setting the guidelines, please consider certain technicalities, such as access to the content of the mailbox once the employee leaves. There might be a few roles that will require reference to those communications. Most organizations cover this in their policy for internal usage for IT and infrastructure. Hence, look for it accordingly.
Regards