External Source: http://blogs.gartner.com/bill-pray/2010/07/15/really-what-does-e-mail-cost/
When determining e-mail costs, it is important to look beyond the licensing costs and to also use, at the least, a three year average to get the best grasp on what it really costs.
Costs should include not only the e-mail licensing, but add-ons, mobile, perimeter services, archiving, and migration costs if you are considering a new e-mail solution.
So, here are two examples of large enterprise’s and their costs – remember your mileage may vary:
A large financial institution with 35,000 plus mailboxes on 60 plus servers (also significant regulatory and compliance requirements) -
A large energy enterprise with 36,000 plus mailboxes, using an older e-mail solution and infrastructure (that is under review for replacement), with some of the servers being hosted by third parties -