In your HubSpot account, you can choose to automatically create and associate companies with contacts based on contact email address and company domain. When enabled, this feature will associate a company to any contact whose email address matches that company's website domain.
Please note: Turning this setting on will associate any current contacts with companies as well as any newly added contacts.
With this setting turned on, HubSpot will look at a contact's email address domain and try to match it to a company's Company Domain Name property to create an association between the two. For example, if a new contact has the email address firstname.lastname@example.org, the contact would be associated with a company whose Company Domain Name is yourcompany.com. If a company does not exist in your account to match the contact's email domain, HubSpot will automatically create a company record and pull in information from our database.
If the contact has a freemail email account (gmail.com, yahoo.com, etc.), HubSpot will also look at the contact's Website URL property to attempt to match the contact with a company's domain name.