In 2013, Gmail changed its interface and email categorization. Because of this change, emails sent by marketing platforms such as HubSpot will appear in the Promotions tab.
Please note that the Promotions tab is by no means the equivalent of a spam folder. It is simply a newer email categorization interface Gmail implemented on its platform.
You'll find that simply dragging the email message from the Promotions tab to Primary will ensure the email is placed there moving forward. Gmail will ask you if you would like to make this permanent, we recommend answering “Yes”.