FastmailApr 23

Fastmail now has an MCP endpoint: https://api.fastmail.com/mcp.
MCP is an open standard, not tied to any one vendor. It sits alongside IMAP, CalDAV, and CardDAV as another way to connect to your email, calendar, and contacts. Optional, OAuth-gated, with read-only, write, and send permission levels.

You pick the client. Your data, your choice.

Read more: https://www.fastmail.com/blog/an-mcp-server-for-fastmail/

#NationalEmailDay #MCP #OpenStandards #Fastmail #EmailPrivacy #BetterEmail

Show threadChris HasenpflugApr 23

@fastmail well, I've tried configuring in a few different tools now. Got it okay in Claude.ai on web to work, but everything local is failing.

```
> opencode mcp auth fastmail

┌ MCP OAuth Authentication
│
■ Authentication failed
│
■ invalid_request no scope
│
└ Done
```

claude cli logs when attempting to authenticate:
```
2026-04-23T03:49:18.353Z [DEBUG] MCP server "fastmail": Returning cached discovery state (authServer: https://api.fastmail.com)
2026-04-23T03:49:18.477Z [DEBUG] MCP server "fastmail": Saving discovery state (authServer: https://api.fastmail.com)
2026-04-23T03:49:18.527Z [DEBUG] MCP server "fastmail": No client info found
2026-04-23T03:49:18.594Z [DEBUG] MCP server "fastmail": HTTP Connection failed after 1436ms: invalid_request no scope (code: none, errno: none)
2026-04-23T03:49:18.594Z [ERROR] MCP server "fastmail" o3T: invalid_request no scope
2026-04-23T03:49:18.595Z [DEBUG] MCP server "fastmail": Connection failed after 1437ms: invalid_request no scope
2026-04-23T03:49:18.595Z [ERROR] MCP server "fastmail" Connection failed: invalid_request no scope
```

codex cli:
```
> codex mcp login fastmail
Error: Registration failed: Dynamic registration failed: Registration failed: HTTP 400 Bad Request: {"error_description":"invalid_request no scope","error":"invalid_request"}
```

Email and calendar made better

Fast, private email hosting for you or your business. More productive, lightning fast, simple and built to save you time.

Fastmail
Show threadFastmailApr 23
@chrishas35 Looks like OpenCode is not sending the required OAuth scopes when authenticating. We are happy to do some additional troubleshooting if you'd like to open a support ticket. fastmail.com/support
Show threadChris Hasenpflug
@fastmail Yes, opencode…and claude cli, and codex cli. Rather curious they'd all be having the same problem, individually... If a scope is required that none do out of the box, it probably should be documented? Perhaps I'll get something logged to support later, but think there's enough in that toot to go on.
Apr 23 at 5:32amWeb
Show threadLeon CowleApr 24
@chrishas35 @fastmail I logged a ticket, Chris. Let's see what they say. I'm getting the same scope errors as you were, even with providing scopes (e.g. urn:ietf:params:jmap:mail). I also tried curl using a bearer token directly, and get an MCP Scope 403 back. I'll let you know what I hear back.
(Or let me know if you made any progress.)