Why is the time on my email wrong?

First, as you point out, your computers time and date must be correct. That's easy to adjust: just double click on the clock in your task bar and you'll get the Date and Time Properties dialog where you can adjust the date and the time:

Notice the "Time Zone" tab? Click on that and make sure your time zone is correctly selected:

Finally, go ahead and click on the tab labeled Internet Time:

Most of the time the default settings are correct, but make sure that Automatically synchronize... is checked to allow Windows to synchronize your clock with an appropriate time server. If your clock "drifts", as some do, this will help keep it accurate.

The preceding steps should correct any time errors in an email client you run on your machine. Programs like Outlook, Outlook Express, Thunderbird, and others all use Windows to determine the time, date, and time zone.

If you're using a web service such as Hotmail, though, you're not quite done.

Hotmail, GMail, Yahoo!, and other web-based services usually ask you for your time zone when you sign up. If you ignore that, get it wrong, or move to a different time zone, you'll need to change the setting in order for the time stamps of your emails to be correct.

For example, once you've logged into Hotmail, click on the Options button in the upper right:

Then click on Personal on the left, for Personal Options, and then click on My Profile, which is described: "Change your name, location, and other personal information."

As I write this, Microsoft is transitioning to "Windows Live" for account management, so the resulting page will be a Windows Live branded page:

If you scroll down that page, you'll find a setting beneath your location where you can specify your time zone:

Press Save, and it's updated.

Services other than Hotmail have similar settings in profile, user account, or personal information settings. Regardless of which service you use, the time zone must be set properly for your email to be timestamped correctly.