In the HubSpot CRM under Settings > Companies, you can choose to automatically create and associate contacts with their company 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: the HubSpot CRM must be enabled in order to use this feature. Turning this setting on will associate any current contacts with companies as well as any newly added contacts.
This setting can also be turned on by navigating to Contacts > Contacts Settings in your Marketing account:
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.