Fastmail MCP server
To connect Fastmail to an AI agent, create a Fastmail API token for mail (and, optionally, an app password for calendars) and paste them into Prubex. Prubex uses Fastmail’s JMAP API for mail and CalDAV for calendars.
Connect Fastmail in 4 steps
- In Fastmail, open Settings, then Privacy & Security, then Connected apps & API tokens, and create a token with Mail and Email submission (read and write).
- For calendars, also create an app password that allows Calendars (CalDAV).
- In Prubex, choose Connect an account, then Fastmail, and paste the token (and the app password).
- Add Prubex to your agent: in Claude or ChatGPT as a connector (you approve it in Prubex), or with an API key for Cursor, VS Code and other clients.
What your agent can do with Fastmail
| Capability | Supported |
|---|---|
| Read mail | Yes |
| Search mail | Yes |
| Conversations | Yes |
| Folders | Yes |
| Drafts | YesEditing a draft saves a new one in its place. |
| Send, reply and forward | Yes |
| Flag, label, move and trash | YesLabels are single lower-case words (JMAP keywords). |
| See what changed | Yes |
| Read calendars | YesCalendars need the optional app password when connecting. |
| Create and change events | Yes |
| Answer invitations | Yes, by PrubexFastmail sends the reply itself; a comment cannot be carried over CalDAV. |
| Propose a new time | No |
| Free/busy | Yes, by PrubexComputed from the account’s own calendars. |
| Attendees’ free/busy | No |
| Online-meeting links | No |
Good to know
Checked .
- Mail runs over JMAP, Fastmail’s own fast API.
- Calendars are optional: skip the app password to connect mail only.
- Labels are single lower-case words, as Fastmail keywords are.
- Fastmail sends invitation replies itself; a comment cannot be carried over CalDAV.
Fastmail questions
Why an API token instead of signing in?
Fastmail registers sign-in for third-party apps on request, and Prubex will move to it when it has one. Until then an API token limited to mail is the safest option.
Do I need the app password?
Only for calendars. Without it Prubex connects your mail, and you can add calendars later.
Can I limit what the token allows?
Yes. Give it Mail and Email submission only; Prubex needs nothing else. You can delete it in Fastmail at any time.