You can now include merge fields in email responses to From submissions that don't have a Lead Magnet.
For example, say you have a custom contact merge field for "Big Project". You can include {{big_project}} in your email response:
Hi-- I'm looking forward to discussing {{big_project}} with you.
You can also include merge fields in the subject line.
Note that if you use fields like {{contact_name}} or {{contact_first_name}}, you'll want to ask for those in the form fields.