If you want to mark whether a booking enquiry has come from an email or over the phone or via a third-party source you can create Sources to mark the enquiry/booking with.
Go to Settings
> Venue Group
> Add Another
> Add "Over The Phone" and "Email" as two new Booking Sources (you can also add any third parties you work with)
> Make sure to SAVE the page.
When you add the enquiry to Collins, in the customers booking details screen, the "Source" drop-down box will pull through all the sources you have added in your admin, with which you can tag your bookings.
In your Enquiries download, you will see a "Source" column if you want to analyse your sources of bookings