Instantly is an email marketing platform that offers basic email marketing features such as email templates, list segmentation, A/B testing, and email tracking. It also includes an easy-to-use drag and drop email builder, responsive email designs, and integration with popular CRMs like Salesforce and HubSpot. On the other hand, SendGrid is a more robust email marketing platform that offers advanced email automation, marketing campaign analysis, and deliverability optimization. It also offers features such as email optimization, email deliverability services, API integrations, real-time analytics, and email validation. In summary, while both platforms offer email marketing services, SendGrid offers more advanced features that allow users to optimize marketing campaigns effectively.