As mobile email providers expand their market to "the next 100 million" users, beyond the 5 million to 6 million corporate users today, systems that automatically send all incoming emails to a mobile device could overwhelm employees and may actually reduce productivity, according to recent user surveys by research firm Strategy Analytics Inc.

" 'Push' email is overrated, in our view," said Cliff Raskind, Strategy Analytics' director of wireless enterprise strategies, speaking today at the Mobile and Wireless World conference in Orlando, Fla.

That finding raises questions about the business model of BlackBerry-maker BlackBerry , which has dominated the corporate mobile email market by providing a high-end, secure solution that pushes all of a user's email directly to the mobile device. As mobile email penetrates deeper into organizations, many less tech-savvy users, according to Raskind, will have trouble managing the flood of email showing up on their mobile devices. (See RIM's Unified Theory.)

"It'll be like the Tom Cruise movie," Raskind said. " 'You can't handle mobile email!' "

The barrage of email on mobile devices means that a premium will be placed on reducing complexity and establishing some kind of filtering mechanism, Raskind added, so that "the right messages get to the right people." Offering solutions without a full push-email capability is also likely to lower the cost of mobile email, bringing it down to $10-$11 per user per month.

For the IT managers in the audience, the question becomes, what -- or who -- is the filter?

Mobile email "is like water," commented Michael Woolfe, network engineer at Unitech, an IT services and training firm in Winter Park, Fla. "Too much and you drown. Not enough and you die of thirst."

In many companies, where mobile email is still limited to top executives, the de facto filter would become a secretary or administrative assistant.

"For instance, the VP only needs to see the emails his secretary shows him," says Woolfe. "She plays a big role -- she has more access because a lot of the time she knows more" than the executive.

Automated filtering systems that use the sender or the subject line to filter out non-urgent mail present their own problems. An email from an IT manager, relatively low down in the corporate hierarchy, might be an urgent request for authority to terminate a user's access to corporate information. One from a person not on the executive's contact list might represent a time-sensitive business opportunity, and so on.

And many end-users prefer to do their own email filtering, says Steve Chase, enterprise architect at H&R Block in Kansas City, Mo.

"I've got 350 users, and maybe four of them have some kind of filter," Chase comments. "The real demand is for a quick delete. That's what good about the [Palm Inc. ] Treo 650."

— Richard Martin, Senior Editor, Unstrung