You can set your forms to not accept email addresses from consumer domains. This helps ensure that customers and prospects only use company emails.

List of Blocked Domains

If set, the validation rule blocks emails with any of these endings:

Instructions

Navigate to Content > Forms and create your form (or edit an existing form)
Add a text box block to the form to accept an email address (or edit an existing text box)
Select the Validation tab
Click + to add a rule
In the IF dropdown, select Non-Consumer Email
Update the error message, if desired
Click OK

You can test this setting by embedding the form in a landing page and entering an email address from one of the domains above.