Resend

Password resets, receipts, welcome messages and notifications are the everyday mail that Resend lets developers send through an API. It positions itself as an email API for developers, covering both transactional and marketing messages at scale.

Sending, receiving and managing mail in code

Resend's own briefing for agents sets out what to use it for. A single request to its emails endpoint, authenticated with an API key, sends a message, and a batch endpoint takes up to 100 messages at a time. Official SDKs, a command line tool and an MCP server provide other ways in. On the marketing side it manages contacts, segments and broadcasts, and recurring flows can be built with automations. Inbound mail works by pointing MX records at Resend and acting on messages through webhooks. Templates can be written in React with the React Email library and then sent through the API.

Domains, webhooks and deliverability

Resend also covers sending infrastructure: verifying domains with SPF, DKIM and DMARC, rotating API keys, configuring webhooks and watching delivery events. Its deliverability guidance explains that spam or Junk placement depends on the sending domain's reputation, content and recipient engagement rather than on Resend's own IP addresses. Separate guides cover Gmail, Outlook and Microsoft 365, Yahoo and iCloud, plus how to warm up a new domain.

Tools for agents, and rules of use

The page lists an agent set-up guide, a remote and a self-hosted MCP server, an agent plugin with skills, and an OpenAPI specification. There is no support API: agents helping a user are told to diagnose, draft and let the user submit the request. Resend states that it must not be used to scrape inboxes or send unsolicited bulk mail, since recipients must have opted in. Enterprise terms and a nonprofit programme have their own pages.