It's best to fully encrypt your laptop or mobile device, since the portability of such devices puts them at special risk of being lost or stolen. For more information on encrypting your Windows computer or laptop, see "How to Encrypt Files With Your Windows PC." For mobile devices it's best to use an operating system that provides full device encryption by setting a PIN or password to protect your email and other data. BlackBerry and iOS (iPhone, iPad, and iPod Touch) devices have offered this type of encryption for years; Android supports it only in version 3.0 and later. For older Android devices, consider obtaining a third-party email app, like TouchDown for Exchange accounts, that provides encryption.
For desktops and laptops, you can encrypt just your email data files if you prefer not to encrypt the whole computer. The encryption features of email clients vary, so check the documentation for your particular program and version. If your email client doesn't offer trustworthy encryption, consider selectively encrypting the directory where your email records are stored.
If you use a Professional, Business, or Ultimate edition of Windows, for example, you can encrypt email records--no matter what email client you use--through Windows' built-in Encrypted File System (EFS) feature. First, find the file(s) that your email client uses to store your email messages; Microsoft Outlook uses a .PST file to store messages, or an .OST file for Exchange accounts. In Windows XP, you'll find the file at C:\Documents and Settings\yourusername\Local Settings\Application Data\Microsoft\Outlook. In Windows Vista and 7, it's at C:\Users\yourusername \AppData\Local\Microsoft\Outlook.
Once you've determined where your email client stores your data, right-click the file(s) or the folder that contains them, select Properties, click Advanced, and select Encrypt contents to secure data.
That's all you have to do. The EFS feature will open and automatically decrypt file(s) when you're logged into your Windows account. Remember to disable encryption before reinstalling Windows or changing your Windows account, or you'll risk being unable to decrypt the files later.
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