The obvious costs of in-house email systems are extensive, but the hidden or indirect costs can prove too much to result in a positive cost/benefit relationship between productivity and in-house email. Other costs can present themselves in a more indirect way, adding to the cost of not only in-house messaging, but the fixed costs of in-house IT, whether you choose to outsource your messaging capability or not.
It isn't exactly fair to call these "hidden costs." The costs themselves are real and openly visible in the budget, but they are often attached to budgets not directly associated with the purchase of new equipment or licenses.
These costs can pertain to IT departments, email management, or any number of additional administrative functions that surround the messaging system.
The obvious cost is of maintaining a staff to deal with the highly technical and specialized skill of server and email management. Even a modestly sized business attempting to operate their own email server will generally have multiple IT specialists devoted to several functions.
