Once you go over your monthly order limit your Shopify notification emails continue to send, but marketing components and analytics may not be supported. Auto follow-up emails will stop sending until you upgrade or your next plan cycle starts.
We warn you at 90% of your plan limit and again once your plan has exceeded its limit. To see the limit on all the plans you can refer to this article http://spently.com/pricing.
If you are worried that you are going to go over your plan limit let us know. We'd be more than happy to discuss with you what is the best plan for you. To do this, send us a message in the chat bubble or reach out to us at firstname.lastname@example.org.