HubSpot's Collected Forms tool allows you to capture form submissions from existing non-HubSpot forms on your website. Collected Forms listens for a submission on a form on your website, which is identified by the HTML
<form> tag. As soon as a visitor submits the form, HubSpot stores the submission information in a cookie on the visitor's browser. This cookie is called li_formsub.
The purpose of this cookie is to ensure that HubSpot can process the submission, even if the form redirects to a new page. In the event that the page redirects, once the contact loads a new page on your site, HubSpot will see the previously set li_formsub cookie and capture the information, removing the cookie in the process. In the event that the page does not redirect, HubSpot will wait a brief moment and then capture the data stored in the li_formsub cookie and remove the cookie.
Once HubSpot captures the form submission from the cookie, a submission notification email will be sent (if enabled) and the contact will be pushed to any connected email provider lists. This process can take approximately two minutes.