# Agent-ready email and messaging Home > Browse > email and messaging 129 verified email and messaging sites, 69 of them transactable — every one probed live, with the date it was checked. Figures generated 2026-09-27T07:19:26.699Z Checks passed across the 140 probed hosts: Markdown negotiation 122 · Markdown twin at a predictable URL 91 · llms.txt 128 · API catalog 36 · MCP server card answers 94. - [Sendmux](https://knowngood.sh/site/sendmux.ai) Sendmux provides an email API for AI agents to send, receive, route, and manage email inboxes with failover and provider routing. - [Email-Check.app](https://knowngood.sh/site/email-check.app) Email-Check.app provides a real-time email validation API for signup flows, CRM hygiene, list cleaning, and deliverability operations. - [PostStack](https://knowngood.sh/site/poststack.dev) PostStack provides a European email API platform with REST, SMTP, and OAuth 2.0 support, hosted in Finland and GDPR compliant. - [Resend](https://knowngood.sh/site/resend-staging.com) Resend provides an email API for developers to send transactional and marketing emails at scale with a modern API. - [Resend](https://knowngood.sh/site/resend.com) Resend provides an email API for developers to send transactional and marketing emails at scale with CLI tools and extensive documentation. - [FormsFort](https://knowngood.sh/site/www.formsfort.com) FormsFort provides a backend service for HTML forms with email delivery, spam controls, file uploads, and webhook integrations. - [Gratis Dansk Chat & Chatrum med Avatarer](https://knowngood.sh/site/www.skyskraber.dk) Skyskraber is a Danish 2D chat platform for adults 18+ featuring avatars, missions, toplists, achievements, and virtual apartments. - [تطوير الحقائب التدريبية](https://knowngood.sh/site/d-tb.org) A leading Arabic site offering over 5000 ready-made and custom training kits with immediate email delivery. - [Generect](https://knowngood.sh/site/docs.generect.com) Generect is a platform for real-time B2B lead discovery and verification with API and CRM integration. - [Maito](https://knowngood.sh/site/getmaito.com) Maito is a newsletter platform for founders, publishers, and creators to build and manage an owned audience with publishing and social promotion tools. - [JetEmail](https://knowngood.sh/site/jetemail.com) JetEmail provides SMTP and API email delivery, inbound filtering, and marketing email services with subscriber-based pricing and unlimited sending. - [OpenMail](https://knowngood.sh/site/openmail.sh) OpenMail provides an email API for AI agents to create inboxes, send and receive emails with real-time webhooks and attachment parsing. - [AhaSend](https://knowngood.sh/site/ahasend.mintlify.app) AhaSend provides developer-first transactional email delivery with REST APIs, SMTP relay, and CLI tools, supporting fast delivery and transparent pricing. - [Fax.Plus API](https://knowngood.sh/site/apidoc.fax.plus) Documentation for Fax.Plus API enabling integration of online fax functionalities into workflows. - [Broodnet](https://knowngood.sh/site/broodnet.com) Broodnet provides real email inboxes for AI agents with inbound from anywhere and controlled outbound sending. - [Z-API Docs](https://knowngood.sh/site/developer.z-api.io) Z-API provides a RESTful API to interact with WhatsApp Web, including message sending and webhook notifications. - [DeBounce API](https://knowngood.sh/site/developers.debounce.com) Technical overview and documentation of the DeBounce email validation API for developers. - [Heymarket API Documentation](https://knowngood.sh/site/developers.heymarket.com) Heymarket REST API enables sending messages, managing contacts, organizing conversations, and integrating with systems. - [EuAtendo API Whats Delphi](https://knowngood.sh/site/doc.apicomponente.com.br) Documentation for EuAtendo API providing WhatsApp integration with test servers and setup instructions. - [Cleariflow API](https://knowngood.sh/site/docs.cleariflow.com) Cleariflow API provides an email validation service that checks email deliverability, format, and quality via an API. - [Connectly](https://knowngood.sh/site/docs.connectly.ai) Connectly provides developer documentation for a WhatsApp Business messaging platform enabling scalable messaging and chatbot automation via API. - [Contiguity](https://knowngood.sh/site/docs.contiguity.com) Contiguity provides APIs for messaging, email, and identity verification with account creation and API key generation. - [EmailBison Docs](https://knowngood.sh/site/docs.emailbison.com) EmailBison Docs provides documentation to get started with the EmailBison API, including workflows and API calls. - [emailr_](https://knowngood.sh/site/docs.emailr.dev) Documentation for Emailr platform to send transactional and marketing emails, manage contacts, and automate workflows via HTTP API. - [Enrichley Docs](https://knowngood.sh/site/docs.enrichley.io) Documentation for Enrichley, an API and platform for email validation, lead discovery, and AI assistant integration over MCP. 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