You can edit the notification settings and add any custom field from the record its self.
Set the message, to "Custom Message"
Then select which field you you would like to insert into the message. Add any verbiage to make it your personalized email, but any information you want to insert from QuickBase, just use the drop-down on the right of the text field.
If you need something a little more customized, you should also look into Juiced Technologies' ExactFormsPlus! and QBCourier tools which have great integration with QuickBase allowing you to generate professional Documents which can then be attached to and send out to customers with customized emails. The QBCourier tool allows you to control where the email is sent from among other things, so customers don't know your data is stored in/comes from QuickBase.