Real time validation is always enabled, however to use real time validation and validate email address as you enter them you must have the Pipedrive setting “Open details panel after creating a new item” checked for the “Person” option.
In this mode, after entering a new contacts details Pipedrive opens the contact detail page. It is at this point that the email addresses can be validated.
To switch this mode on, go to Pipedrive “Personal Preferences” and scroll down to the “Interface” section. Select “Person” under “Open details panel after creating a new item”.