But, as at many organizations, the wall guarding the e-mail systems at Larsen's company—travel agency Groople—is constantly under siege, with the attacks getting more brutal.

"As Groople has grown, I have seen the volume of e-mail-based attacks skyrocket," said Larsen, the company's manager of IS. "It soon overburdened our e-mail gateway, and I was forced to implement new systems and software to handle the huge increase."

Vendors and enterprises alike are faced with a new e-mail threat landscape, where spam is increasingly laced with malware and targeted attacks have become more common. IT pros have a lot to consider—both in terms of technology and best practices—as they deal with the growing e-mail security challenge.