There is the option to enter a Primary and Secondary email address for staff on their Profile; click on the cog next to their name to access Personal Details.
Schools often use the school email address as the primary, and the Secondary Email is their private email.
If you need to enter email addresses for a large number of staff, go to Admin > Personnel > Staff Group Updater.
Click on Select a Staff Attribute and type 'email'. This will filter the available options, and you are offered the opportunity to select either Primary Email or Secondary Email. Then click on Choose.
A table with all staff will appear. Tick in the Select box for the individual staff you wish to enter the emails for, or Check All to select them all. Enter the email address in the Value column, then Update Staff to save. The email addresses entered here will now appear in the Personal Details field on the Staff profiles.