Postgate AI - Microsoft Exchange MCP Server

MCP server for Microsoft Exchange Server SE: on-prem (EWS) & hybrid.

Postgate AI exposes Exchange mailboxes as an MCP server, with 90+ tools over Streamable HTTP, OAuth 2.0/PKCE, and delegated per-user permissions. Mailboxes in your own network are connected via EWS, for Exchange Server Subscription Edition (SE) plus Exchange 2019 and 2016. Mailboxes in Exchange Online are reached via Microsoft Graph. Either fully managed in Germany or self-hosted under license.

Architecture

The technology in seven points

The MCP standard

Model Context Protocol is the open standard that AI assistants use to reach external systems. Postgate AI exposes Microsoft Exchange as an MCP server for Claude, ChatGPT, Perplexity, Mistral Vibe, and any other MCP-capable client. We fully support the July 28, 2026 revision. Older clients keep working exactly as before, so there is nothing for you to change.

Transport: Streamable HTTP (July 28, 2026 revision)

We implement the July 28, 2026 MCP revision on the server side, with exactly one endpoint: /mcp. The new revision drops three things, and all three used to cost time: the session ID, the handshake before the first tool call, and the permanently open stream per client. Every request now stands on its own. For self-hosted setups, that means several nodes behind a plain load balancer, no session affinity, and one more node as soon as load grows. A restart no longer cuts anyone off. TLS on every route, and no client needs Server-Sent Events anymore.

Sign-in: OAuth 2.0/PKCE, Entra ID or AD FS

Verified identity instead of trust-based headers: clients authenticate via OAuth 2.0 with PKCE, self-service onboarding via Microsoft sign-in or a one-time code from the portal. Out of the box, sign-in runs through Microsoft Entra ID, which also fits a hybrid setup. If you want no cloud sign-in at all, point us to your own AD FS as the issuer, and we validate tokens from your own environment. Mailbox access runs natively over the Windows sign-in (NTLM) or, once Exchange trusts your own issuer, over modern auth with a per-user token, with no domain password in the vault.

Per-user vault

Exchange credentials are stored RSA-4096-encrypted per user in a vault in Germany. Delegated access with existing Exchange permissions, no service account, no application impersonation.

Connected via EWS and Microsoft Graph

Mailboxes on an Exchange Server in your own network are connected via EWS, for Exchange Server SE, 2019, and 2016. Mailboxes in Exchange Online are reached via Microsoft Graph. Both run side by side in the same setup, and every organization sets for itself which one applies. A cloud mailbox is not a requirement.

Several nodes behind one load balancer

The current MCP revision works without session affinity. Several instances can therefore run side by side, and each request goes wherever there is room. When the number of users grows, you add another node.

90+ tools

Mail, calendar, contacts, tasks, folders, attachments (incl. PDF/DOCX/XLSX extraction), threads, global address list, free/busy times, and semantic search. The entire mailbox as a toolbox.

Integration

One MCP server, three ways to use it

AI assistants

Claude, ChatGPT, Perplexity, and Mistral Vibe, desktop and mobile. Gemini via Gemini Enterprise or Google Antigravity.

Agent platforms

Microsoft Copilot Studio plugs Postgate AI in as an MCP tool. Your Copilot agent then works with on-premises mailboxes. The same goes for n8n and for any other platform that speaks MCP with OAuth.

Custom agents

Any MCP-capable runtime can use the tools, from a Python script to a full agent platform.

Step-by-step guides: Claude, ChatGPT, Gemini, Perplexity, Mistral Vibe →

Landscape

Microsoft Exchange MCP servers compared

Other MCP servers

Most MCP servers for Exchange speak Microsoft Graph only, so they reach mailboxes in Exchange Online and nothing else. An Exchange Server in your own network stays out of reach.

Postgate AI

We connect Exchange on-premises via EWS, and Exchange Online via Microsoft Graph on top of that. Both run in the same multi-user server, either fully managed or self-hosted under license. OAuth 2.0/PKCE, a per-user vault, and central administration are included, set up once for all employees.

FAQ

Frequently asked questions

What is an MCP server for Microsoft Exchange?

A server that makes Exchange mailboxes accessible to AI assistants via the Model Context Protocol (MCP): emails, calendar, contacts, and tasks as standardized tools that Claude, ChatGPT, Mistral Vibe, or custom agents can call, with the permissions of the respective user.

Does the MCP server work with Exchange on-premises?

Yes, that is the core: connection via EWS for Microsoft Exchange Server SE, 2019, and 2016, including hybrid environments. Either fully managed or self-hosted under license, in both cases with no installation on clients.

Can I use the MCP server in Copilot Studio or n8n?

Yes, both work. In Microsoft Copilot Studio you add Postgate AI as an MCP tool (Streamable HTTP, OAuth 2.0 with dynamic discovery) and your Copilot agent then reaches on-premises mailboxes. n8n works the same way. In both cases every user works with their own Exchange permissions.

How do users authenticate?

Clients via OAuth 2.0 with PKCE; the user’s Exchange credentials are stored encrypted in the per-user vault. Every access is delegated, using the existing Exchange permissions of the respective user.

How is Postgate AI different from open-source MCP servers for EWS?

Open-source servers usually run as a stdio process for a single mailbox, with credentials in environment variables and self-managed operation. Postgate AI is a multi-user MCP server with OAuth 2.0/PKCE, an RSA-4096 vault per user, delegated permissions, and central administration in the portal, either fully managed or as a self-hosted license.

Exchange as an MCP server, ready to try in minutes.

Free for 14 days on the fully managed plan: connect your EWS URL, pair a client, and use the tools. Contact us for a self-hosted license.