How to Connect Multiple Outlook Calendars to Codex
Codex has no first-party Outlook connector, which turns out to be an advantage here. Because calendar access arrives through whichever MCP server you register, the one-identity ceiling that stops the built-in connectors in other assistants is not something Codex imposes. Two tenants is a configuration problem, not a wall. Carly holds your Google calendars and every mailbox on both sides in the same place, so this setup covers the rest of what you own.
Codex is a coding agent, so the honest framing stays the same: this is for a developer who wants schedule context in a terminal. Recurring scheduling belongs in a workflow that runs without a session open.
Shared mailbox or separate identity?
Sort this first, because it decides whether you need any of this.
| What you have | What it needs |
|---|---|
| Several calendars in one Microsoft 365 account | Nothing special, one authorization covers them |
| A shared or delegated calendar your account can already open | Usually the primary identity’s existing access |
| A second Microsoft 365 login | A separate authorization |
| Accounts in two tenants | A separate authorization per tenant |
Rows three and four are the reason for the rest of this guide. A guest account in a client tenant counts as a separate identity even though it lives in the same Outlook app on your laptop.
Why one MCP server beats one per tenant
The common approach is a third-party MCP provider such as Composio, Merge, or Nylas, one server per account. Three tenants means three server entries, three OAuth apps to maintain, and nothing in the prompt vocabulary that distinguishes them, so the agent picks whichever loaded first.
Carly inverts that. Each Microsoft identity is authorized once inside Carly, and Codex sees a single server that addresses any of them by email address. Adding a fourth tenant changes nothing in config.toml.
1. Label each calendar by tenant
All addresses below are fictional.
| Address | Role |
|---|---|
fictional.dana.whitfield@pepsi.com | Main Company |
fictional.dana.whitfield@ford.com | Consulting |
fictional.dana.whitfield@outlook.com | Personal |
Use the role in ordinary queries and the full address before anything that writes.
2. Connect every Microsoft identity to Carly
- Sign in at carlyassistant.com.
- Open carlyassistant.com/integrations.
- Find Outlook and click Connect.
- Sign in with the first Microsoft 365 identity and approve access.
- Confirm the connected address in Carly.
Repeat for every additional tenant, choosing Use another account if Microsoft preselects the first login. Verify the full address after each authorization.
If Microsoft displays Need admin approval, that tenant’s Entra administrator approves the connection. On a client tenant you do not control, start this early rather than at the end.
Unlimited connected emails and calendars are included on the $35/month plan, so the third and fourth tenant cost nothing extra.
3. Register Carly as an MCP server
codex mcp add carly --url https://carlyassistant.com/mcp/Servers added this way land in ~/.codex/config.toml at user scope. The manual entry is equivalent:
[mcp_servers.carly]
url = "https://carlyassistant.com/mcp/"A trusted project can carry its own .codex/config.toml if you would rather scope the server to one repository.
Then authenticate:
codex mcp login carlyComplete the OAuth flow in the browser, signing in to the Carly workspace holding the calendars. Codex supports OAuth and bearer-token auth against remote HTTP MCP servers, so nothing goes into the config file as a secret.
Confirm it is live:
codex mcp list4. Test each calendar read-only
Start a new session so the tools load, then take one tenant per prompt:
On
fictional.dana.whitfield@pepsi.com, list this week’s meetings with times and organizers. Do not change anything.
On
fictional.dana.whitfield@ford.com, show everything booked in the next five days. Read only.
Then the cross-tenant question:
Compare both work calendars for next week and list every conflict, showing the source account for each meeting.
If the tools are missing, start a fresh session. Codex loads a newly installed server’s tools at session start, not mid-session.
5. Reuse this routing prompt
Treat
fictional.dana.whitfield@pepsi.comas Main Company,fictional.dana.whitfield@ford.comas Consulting, andfictional.dana.whitfield@outlook.comas Personal. When finding a time, check all three for conflicts. Always state the target calendar before creating, moving, or cancelling. Never write to a calendar I have not named.
Then name the target per action:
Find sixty minutes next week free on all three and book it on Main Company.
Move the Thursday Consulting review to the first open slot the following week.
Keep approvals on while testing. A coding agent holding write scopes on two employers’ calendars is worth a confirmation step.
Third-party Outlook MCP versus Carly in Codex
| Need | Per-tenant MCP server | Carly MCP server |
|---|---|---|
| Reach one calendar | Yes | Yes |
| Reach several tenants | One server per tenant | One server, all tenants |
| Address a specific account in a prompt | No shared convention | Yes, by email address |
| Find a time free across every account | No | Yes |
| Manage your own OAuth app and scopes | Often required | No |
| Add a fourth tenant later | New server entry | No config change |
| Keep the work running outside Codex | No | Yes |
Free Zapier-style workflows; AI agents from $35/month. Connect it on the integrations page, or start with Outlook.
Quick fixes
| Problem | Fix |
|---|---|
| Tools do not show up | Start a new Codex session after adding the server |
codex mcp login never completes | Finish the browser OAuth flow, then rerun codex mcp list |
| Microsoft reopens the first account | Choose Use another account and reconnect |
| Microsoft shows Need admin approval | Ask that tenant’s Entra administrator to approve Carly |
| A shared calendar is missing | Confirm the primary identity can open it in Outlook |
| Events land on the wrong calendar | Use the full address and require confirmation before writes |
Frequently asked questions
Does Codex have a native Outlook Calendar integration?
No. Codex reaches Outlook through the Model Context Protocol rather than a built-in connector, so what it can do depends on which MCP server you register.
How many Outlook calendars can this reach?
As many as you authorize in Carly. Codex connects to one server, so the tenant count is a Carly setting rather than a Codex one.
Is a shared calendar a second account?
No. A shared or delegated calendar relies on access already granted to a primary identity. Only a separate login or tenant needs its own authorization.
Can Codex find a time that works across two employers’ calendars?
Through a server that holds both, yes. Per-tenant servers cannot, because nothing in the setup lets one query span them.
Related: Codex + Outlook Calendar · Multiple Google Calendars in Codex · Multiple Outlook accounts in Codex · Multiple Outlook calendars in Claude · Best AI assistants for multiple calendars
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