Only administrators or owners may change the password for a POP-only mailbox. Users of POP-only email accounts must request new passwords from administrators.
To change a password:
Email Control Panel: Edit User Link
Verify Security Key Screen
Email Control Panel: Edit User - Change Password Link
Email Control Panel: Edit User - New Password
Email Control Panel: Edit User - New Password Confirmation
Please note that changing a password will prevent the mailbox user from sending and receiving mail until the user changes POP settings to reflect the new password, so be sure to notify the user of any changes immediately.