Short answer

HubSpot's KB: Allow submissions without email addresses to create contacts applies to future submissions. Without email, dedupe uses the tracking cookie, so duplicates are possible. These contacts can't get marketing email. Not for non-HubSpot forms.

1. In HubSpot

The relevant screen in my demo portal.

Form General settings with automatically create new contacts, set new contacts as marketing contacts, and pre-populate fields — New contacts (1), marketing contacts (2), and pre-populate (3).

2. Worth knowing

Expect more duplicates and plan cleanup.

3. Related

New email contacts.

Sources

HubSpot Community question: Managing One Contact with Multiple Email Addresses
HubSpot Knowledge Base: Allow form submissions without email addresses to create contacts

Create contacts from forms without an email

Short answer

1. In HubSpot

2. Worth knowing

3. Related

Sources

New field notes by email

Still stuck?