These rules are from Hotmail, because all internet email accounts should have the same rules..
Change your password often. The quick act of changing your password can ensure your email remains private. In addition, passwords that use both letters and numbers are harder to break.
Don't share your password. Most email administrators will not ask for your password. Do not be duped by malicious emails asking you for your password. This is a well-known, although not-too-common trick designed to fool you into sharing your password. As a rule, never share it with anyone.
Never open attachments from unknown sources. They may contain what are known as "letterbombs" or "viruses," which can damage your PC.
Always remember to log out when you are done. It's quick, easy and may save your account from unwanted trespassers. If you are using a public terminal, at an internet cafe for example, it is advised that you close the browser you were using when you are ready to end your Internet session.
Don't reply to unsolicited messages ("spam") mail, or other harassing or offensive mail. By responding, you only confirm that you are a person with an active email address who can be plagued with constant unwanted email solicitations. Instead, forward the unsolicited message to the customer service department of the source's email (usually of a form similar to abuse@[implicateddomain].com). To help control spam, Hotmail provides members with "filters" for incoming mail. These can easily be set up to send certain messages (such as those that include certain words) directly to your online trash can.
Make sure that you are using the most up-to-date Internet software (e.g. browsers such as Microsoft Internet Explorer or Netscape Navigator). More recent versions often offer enhanced security protection.
Always use a secure network. Most corporate networks and Internet service providers are protected by administrators who watch for potential security problems and act to protect users from "hackers" (malicious users) who may try to steal personal information that is transferred through the network. Although the risk is small, use caution when on any unfamiliar network. Use stations maintained by sources you trust, or ask if the Internet terminal you are using is protected against security break-ins.
Use common sense when you're on the Internet and maintain a healthy dose of skepticism. Use caution when revealing personal information, such as your physical address, to anyone you meet in cyberspace; even if they claim to be someone of authority.