Question: Is there an API that provides instant email and event data upon user connection, and also supports webhooks for real-time notifications?

If you want an API that offers immediate email and event data when a user connects, along with support for webhooks for real-time updates, Nylas could be a good option. Nylas provides a unified API platform for connecting email, calendar and contacts into your app, and it's designed to offer a unified experience for your users. The service offers immediate responses, 99.9% uptime and webhooks for real-time updates. That makes it a good fit for CRM, ATS, HCM, UCaaS, ERP and SaaS apps, and it supports many programming languages with code examples and a free tier for up to 5 accounts.

Another good option is Ably, which provides a real-time digital experience platform with APIs for live chat, data broadcasting and real-time data synchronization. Ably supports a publish/subscribe messaging pattern over WebSocket connections and offers high availability with a 99.999% uptime SLA. The service is designed for high scale and offers libraries for many client and server languages, including React, PHP, iOS and Web. It also offers certifications like SOC 2 Type 2, HIPAA compliance and EU GDPR certification.

If you want to gather event data from multiple sources and integrate it into your app, Jitsu is a good option. Jitsu pulls data from the web, apps, email and CRM systems into a data warehouse, offering real-time event streaming and unified data storage. The service can integrate with multiple data warehouses, and pricing is flexible, including a free tier. That makes it a good option for developers who want to build sophisticated apps with real-time data processing.

Finally, Twilio is a general-purpose customer engagement platform that includes communication APIs for SMS, WhatsApp, voice and email. Twilio's Email API lets you send transactional and marketing emails at scale, and it can send real-time notifications through webhooks. More than 290,000 brands use Twilio, so it's a tried and true option for customer engagement needs.