Email MCP servers are starting to split into a few distinct categories. Some help AI agents send product emails from a SaaS application, some provide agent‑owned inboxes, and others connect agents to existing Gmail or Outlook accounts. This guide compares the best email MCP servers and APIs for AI agents in 2026 by looking at their real architecture: MCP support, API capabilities, sending, receiving, agent‑owned inboxes, webhooks, authentication, and fit for production use. Sidemail, Resend, ...