Adding a secondary email account to a control panel user isn't mandatory, however it is extremely useful if that person forgets their username or password, as this is the address that we will send a password reset email to.
To do this, select Users from the top menu and then the user that you wish to edit.
From the yellow menu bar, select Contact Info and then edit.
In the Secondary E-mail field, enter the backup email address. This shouldn't be the same as the email address for their main account as this is likely to be the one that they are having problems accessing!