New contacts will be added to your account if they are added via a web form automatically. If your web form is set up to automatically add the contact to a campaign, the contact will count against your monthly allotment of contacts that can be subscribed to a campaign per your subscription.
What happens if I am over my monthly allotment for campaign slots and a new contact is added via web form?
MDC DOT will add the contact to your account and add them to the campaign, and the system will notify you that your account is over its limit and give you 3 days to make space and remove contacts from other campaigns to get your account under your limit. If you do not do this within 3 days, your account will be auto-upgraded to the next subscription level, and your card on file will be charged the prorated amount.