Spam may be cheap for the people who send it, but it can be a serious expense for your business. According to a study conducted earlier this year by Nucleus Research Inc., spam management costs U.S. businesses more than $71 billion annually in lost productivity — $712 per employee.

Here's a quick look at the various ways that spam drains your company's bank account and how you can calculate the real cost to your business.

Anti-Spam Technology: Spam-fighting products and services are a big business, and anti-spam vendors aren't generating their revenue from the people sending junk email. Most companies not only spend thousands of dollars on anti-spam software and hardware solutions, but they also drop cash on employees and consultants to plan, deploy and maintain the technologies.

Lost Productivity: Spam wastes employees' time. The average employee spends 16 seconds reviewing and deleting each spam message, according to Nucleus Research. The company estimates that at businesses that quarantine spam (where junk messages are placed in a directory for review and confirmation by recipients), each user spends an average of 4.5 minutes per week reviewing messages. Deleting messages, however, turns out to be the most expensive spam strategy. The average employee at companies that delete spam messages loses an average of 7.3 minutes per week looking for lost legitimate messages.