Has this ever happened in your office? Mary e-mails a memo to everyone in the company. May responds with a self-incriminating reply, intended only for Mary, that also goes out to everyone in the company.

Everyone knows not to hit Reply to All indiscriminately, but many people ignore the danger lurking in the innocent-looking Reply button. In many e-mail clients, the author of the original message can easily designate a mailing list as the reply-to address. This technique is commonly used by mass-marketers and other spammers to shield themselves from angry replies from individuals who want to be removed from the mailing list or who call the senders unsavoury names. The solution is simple. Whenever you click Reply to answer a message, always pause and take a close look at the e-mail address that pops up after To: in your message header. If you see multiple names or what appears to be the name of a mailing list rather than a person's name, don't click that Send button unless you're willing to endure the consequences.