While you can't set a password for your entire Outlook program, you can set a password for an Outlook Data File (.pst). This password is required whenever you open the Outlook Data File (.pst).
Not every email account uses an Outlook Data File (.pst) to store your email, calendar, contact, and task information. Many types of email accounts, including Office 365, Exchange accounts, Outlook.com accounts, and many POP and IMAP accounts use Offline Outlook Data Files (.ost) instead. You cannot set a password on an Offline Outlook Data File (.ost).
Note: The steps in this file will not help you reset your password with your email provider. If you forget your email account password, for example, your Outlook.com password, you'll need to contact your email provider for assistance. For more information about changing your email password in Outlook, see Change or update your email password.
Caution: If you set a password on your Outlook Data File (.pst) and forget the password, there is no way to retrieve the password.
Click the File tab.
Click Account Settings, and then click Account Settings.
On the Data Files tab, click the Outlook Data File (.pst) for which you want to change the password, and then click Settings.
Click Change Password. You will not see this option if you've selected an Offline Outlook Data File (.ost) file. The extension of the file is listed in the Location column of the Data Files tab. There is no way to set a password on an Offline Outlook Data File (.ost).
Note: The Change Password button doesn’t appear if you are using an Offline Outlook Data File (.ost) file. Many email accounts, including Exchange, Office 365, and Outlook.com accounts use Offline Outlook Data Files (.ost).
In the Change Password dialog box, type the existing password in the Old password box. If there is no existing password, leave this box blank.
In the New password and Verify password boxes, type the new password. The password can be up to 15 characters and is case-sensitive.
Click OK to set the password.
Important: If you forget your password, Microsoft can’t retrieve it. There is no password recovery option.
Security Note: For a better way to restrict access to your data, use a password-protected Windows user account for each person who uses the computer. For more information, see Windows Help and Support.