If spam has a bright side, it's that the universal annoyance this unwanted e-mail causes everyone from the loading dock manager to the chairman of the board makes it easier for IT to win spending approval for tools to help fight the beast.

Spam's strain on corporate coffers isn't just in lost productivity, which some companies report can be in the hundreds of thousands of dollars per year. It also steals from bandwidth, network storage  and end-user support. And the cost of spam doesn't stop there, considering the potential damage to a corporation's brand or possible litigation arising from the exchange or receipt of questionable e-mail.

Even though selling the benefits of spam blockers can be fairly straightforward given that they must deal with a flood of junk mail, experts say accurately documenting the cost of spam can help IT secure a larger budget and ensure that an effective system is put in place.

"You want to make a Cadillac decision, not a Hyundai decision," says Tom Pisello, founder and CEO of consultancy Alinean, which assesses the business value of IT investments. He says good spam filtering systems can reduce the productivity losses associated with spam by 40% and the associated IT costs by 70%.

There are dozens of anti-spam products and services to consider, such as e-mail appliances, filtering software and hosted services.

"Midsized and large companies need a more sophisticated system than smaller companies, and that's why you have to do your due diligence. A business case is going to be needed for any purchase over $50,000," Pisello says.

And that is the low end. Effective spam-filtering products can run into six figures.

IT managers who do the work to document their needs also are those more likely to gain the benefits such as payback on anti-spam products within six months or less and a ROI of well over 300%, Pisello says.

Quantify costs

Where does the assessment start?

Most IT managers build their case on four key areas: productivity, bandwidth, storage and help desk support. While lost productivity is an obvious area where spam takes its toll, users shouldn't ignore that spam can consume up to 11% of a company's bandwidth and up to 500G bytes of storage each year, according to Alinean. Spam also can generate up to five extra help desk calls per day, per 100 users, which can mandate the need for extra staff.