Imagine being on the receiving end of thousands of e-mail messages because someone put your address in one of these appeals. Once begun, there is no way to recall these chain letters and petitions. The result can be devastating. Don't send large attachments via e-mail. Many mail systems won't accept attachments larger than 2 Megabytes.
Large attachments can clog the recipient's mailbox.
Don't execute programs mailed to you by strangers or which have unclear origins. One of the biggest advantages to the Internet is that it allows for tremendous freedom of speech. Not everyone will use this freedom responsibly. It can be extremely difficult to distinguish fact from fiction, truth from delusion, or honesty from deception. Like a reporter you should look for confirmation by independent and reliable sources before you believe, invest or report to others.