The most surprising aspect of the David Petraeus scandal is that powerful and otherwise bright people were tripped up by e-mail, of all things.

Many key figures in the scandal appear to have washed out on the first day of e-mail boot camp. This is 2013, and e-mail has been a workplace institution since the mid-1990s. Even if the main players did not necessarily send out e-mails from work, the personal e-mails are devastating their professional careers.

Smart people are still getting tripped up by the most basic cyber-reality -- that e-mailing is not a confidential or secure way to communicate. Why are people losing their careers over personal matters revealed in e-mail?

A brief review: CIA Director Petraeus exchanged many "explicit" e-mails with his biographer, Paula Broadwell. She sent harassing e-mails to Jill Kelley, who was close to Petraeus. This prompted a complaint and investigation by the FBI, which stumbled upon the Petraeus-Broadwell affair. An investigating FBI agent sent inappropriate photos of himself to Kelley via e-mail. The commanding general in Afghanistan, John Allen, also appears to have sent "potentially inappropriate" e-mails to Kelley.

Petraeus was forced to resign, the FBI agent is under investigation, and both Broadwell and Allen are facing unfavorable professional scrutiny. The old party game of telephone has become an e-mail circular firing squad.

Here's the legal lowdown: In the workplace, employees have virtually no reasonable legal expectation of privacy with their e-mails. The e-mails that one gets and sends at work are courtesy of the employer's computer servers, which it owns.

This property right has been used to justify how businesses control electronic communications. Employers have been savvy for years in letting their workforces know upfront that they can and do monitor e-mails at work, and have set up many policies for what is and is not acceptable e-mail and Internet use while at work.

If an employee has been working from home and retrieves e-mail from work, or sends e-mails to work from home, they can open themselves up to having their personal computers searched in the event of a lawsuit. The threshold for allowing most civil-litigation discovery is relevance or the potential to lead to relevant information. This can be easily met.

In the Petraeus scandal, the FBI was investigating possible criminal activity, and again, a low threshold for searching electronic information is firmly established in the law. The Electronic Communications Privacy Act allows subpoenas approved by a federal prosecutor, not a judge, to obtain e-mail at least six months old.

But little of the Petraeus scandal e-mail seems to have originated at work, so why are so many careers damaged? Appointive public positions are like most private employment settings; they are "at will," meaning that employers can discipline or fire employees for essentially making the employer look bad. As long as the discharge is not based on discrimination or retaliation, the at-will doctrine generally will provide a stout defense for the employer. Even conduct off-duty can form legitimate business reasons for employment termination. Where there is a connection between the inappropriate behavior involved and the essence of the employer's business, this is especially true.

E-mailing in the workplace has been prevalent since the mid-1990s. It is almost trite these days to cite e-mail figures. No one would be terribly surprised to hear that 247 billion e-mails are sent and received each day, by one recent estimate. The Petraeus scandal is a stark reminder to all employees -- from four-star generals on down -- that e-mails cut everyone the same way.

Phillip J. Trobaugh is a lawyer in St. Paul.