Junk email may be costing your company more than you think; here’s how to add up the real costs.

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 Businesses more than £150 billion annually in lost productivity — £1400 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.

Wasted Storage: Companies that quarantine spam must add extra storage capacity to accommodate suspicious mail so that users can review it at their leisure. But many users never bother to review their quarantined messages, so the email just sits there, consuming storage space and money.

Internet Service Cost Pass-Alongs: This number is difficult to calculate. Still, it would be naive to believe that ISPs aren't passing along junk email's tremendous costs to their customers. In an October 2007 report, anti-spam software vendor Symantec Corp. estimated that 70 percent of all email was spam. The traffic burden created by junk email forces ISPs to add extra network and server capacity, as well as to install their own anti-spam solutions.

An Intangible Cost: Spam has a broader economic impact as well, hitting many businesses and nations that are least able to bear the burden. Consider Nigeria, for example. Nucleus Research noted that while fraud and corruption have been rampant in Nigeria for some time, the country may be forever kept in the digital darkness because of the volume of deceptive email sent by local spammers. The research firm noted that most spam filters block any mail with "Nigeria" in the title or text, effectively keeping anyone communicating with, from, to or about Nigeria from doing it via email.

Your Cost: If you're interested in seeing just how much spam is costing your business, use Computer Mail Services Inc.'s spam-cost calculator. For a second opinion, check out the Sendio spam-cost calculator.

Other spam-cost calculators are available at NetworkWorld.com, Network Computing and Commtouch.