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-account 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.
1. Add your Outlook calendars to Carly
- Sign in at carlyassistant.com.
- Open carlyassistant.com/integrations.
- Find Outlook Calendar, click Connect, and authorize the calendar.
- Click Connect again for the next one, and keep going for as many calendars as you want.
Repeat for every additional account, choosing Use another account if Microsoft preselects the first login.
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 account cost nothing extra.
Carly connects to thousands of apps, so while you are on that page you can add your inboxes, files, CRM, and anything else you want Codex to reach through the same connector.
2. 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 listShared mailbox or separate account?
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 account’s existing access |
| A second Microsoft 365 login | A separate authorization |
| Accounts in two tenants | A separate authorization 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.
Third-party Outlook MCP versus Carly in Codex
| Need | Per-tenant MCP server | Carly MCP server |
|---|---|---|
| Reach one calendar | Yes | Yes |
| Reach several organizations | One server per tenant | One server, all of them |
| Find a time free across every account | No | Yes |
| Manage your own OAuth app and scopes | Often required | No |
| Add a fourth account 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 account can open it in Outlook |
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 account 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 account. 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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