It’s obvious that optional form fields will not always be filled by your form users, yet those fields will appear in your email notification by default. Perhaps you’ll want to hide empty fields that don’t contain any data from your submitters.
If you want to hide empty fields in your email notification, go to the Settings → Notifications section of your form. In Form Owner Options → Other Options, check the option Do not show empty fields in the email notification. This will exclude all input fields that haven’t been filled out by the respective submitter.
In case you want to exclude checkboxes that haven’t been selected, enable the option Do not show unselected checkboxes in the email notification. Upon enabling this option, you can opt to add all selected items in a single line.