Outlook

Overview

The Outlook connector uses Microsoft Graph subscriptions to watch mail folders and calendars. When a message lands or a meeting is booked, Graph notifies Tessel and the change becomes a typed event with sender, folder and attachment details. Replies keep the conversation ID, so the thread stays intact for the person reading it.

Teams use it to file supplier invoices from a shared mailbox into Xero, to book onboarding sessions when Workday marks a hire as started and to forward escalations to a Teams channel.

Supported mailboxes

• Exchange Online user and shared mailboxes

• Microsoft 365 Business and Enterprise plans

• Outlook.com personal accounts for testing

How subscriptions work

Tessel creates a Graph subscription per folder or calendar. Graph posts a lightweight notification, and Tessel fetches the changed item with a delta query so each message is processed once, in order. Notifications are validated with the client state secret Tessel set when subscribing.

POST /v1.0/subscriptions
{
  "changeType": "created,updated",
  "resource": "users/ap@acme.com/mailFolders('Inbox')/messages",
  "notificationUrl": "https://hooks.tessel.dev/graph",
  "expirationDateTime": "2026-10-09T09:00:00Z"
}

POST /v1.0/subscriptions
{
  "changeType": "created,updated",
  "resource": "users/ap@acme.com/mailFolders('Inbox')/messages",
  "notificationUrl": "https://hooks.tessel.dev/graph",
  "expirationDateTime": "2026-10-09T09:00:00Z"
}

POST /v1.0/subscriptions
{
  "changeType": "created,updated",
  "resource": "users/ap@acme.com/mailFolders('Inbox')/messages",
  "notificationUrl": "https://hooks.tessel.dev/graph",
  "expirationDateTime": "2026-10-09T09:00:00Z"
}

Renewal

Mail subscriptions last just under seven days. Tessel renews them a day early and runs a delta query after each renewal to catch anything sent in between.

Permissions needed

Connect with delegated OAuth for one mailbox, or with application permissions to cover shared mailboxes. Use an application access policy in Exchange to limit Tessel to the mailboxes it needs.

• Mail.Read for mail triggers

• Mail.Send and Mail.ReadWrite to send, reply and move messages

• Calendars.ReadWrite for calendar triggers and events