Send Outlook messages from another user

Exchange Online provides mailbox permissions that allow a user to send mail that appears to be sent from another user, distribution list, group, resource, or shared mailbox. Microsoft Graph supports this feature as well, but the end result varies depending on the exact permissions granted in Exchange Online and which API you use to send the mail.

Permissions

Two types of permissions apply to sending messages from another user:

• Microsoft Graph permissions
• Mailbox permissions

Microsoft Graph permissions

In order to send messages from another user, applications that use user tokens use the Mail.Send.Shared permission.

Mailbox permissions

Two permissions affect the end result of sending a message from another user: Send on Behalf and Send As. The user that is signed in to your application with the Mail.Send.Shared permission MUST have at least one of these permissions granted to the mailbox, group, or distribution list that the mail is from.

Send on Behalf

With this permission, the recipient of the email has an indication in their email client that the user of your application sent the message on behalf of another user.

This is exposed in Microsoft Graph as the sender (the user that actually sent the message) and from (the user, group, or so on, that the message appears to be from) properties.

{
  "id": "AAMkAGE1...",
  "subject": "Send mail test",
  "sender": {
    "emailAddress": {
      "name": "Adele Vance",
      "address": "[email protected]"
    }
  },
  "from": {
    "emailAddress": {
      "name": "Pradeep Gupta",
      "address": "[email protected]"
    }
  }
}

A user can grant this permission for their own mailbox to another user by using Outlook. Administrators can grant this permission for any mailbox, group, or distribution list in the Microsoft 365 admin center.

Send As

With this permission, there is no indication that the message was sent as a different user. The sender and from properties have the same value.

Users cannot grant this permission to their mailboxes. Admins can grant this permission in the Microsoft 365 admin center.

Sending with Microsoft Graph

You can send messages from another user by either sending directly or by creating a draft and then sending it.

In order to send from another user, set the from property on the message sent to the email address of the user to send from. You don't need to set the sender property - Microsoft Graph sets it appropriately, based on the mailbox permissions granted to the user who has signed in.

For example, to send mail from the [email protected] group, configure the message as follows.

{
  "subject": "January sales report",
  "toRecipients": [
    {
      "emailAddress": {
        "address": "[email protected]"
      }
    }
  ],
  "from": {
    "emailAddress": {
      "address": "[email protected]"
    }
  }
}

Sent Items behavior

After the message is sent, it can be saved to the sending user's Sent Items folder, the from user's Sent Items folder, or both. It can also not be saved at all.

• If your application sends by using the /me endpoint (or /users/{user-id} where the user-id corresponds to the signed in user), by default, the message will be saved in the sending user's Sent Items folder.
• If your application sends by using the /users/{user-id} where the user-id corresponds to the from user, by default, the message will be saved in the from user's Sent Items folder.

  Important

  In order to send this way, the sending user must have the Full Access mailbox permission in addition to either the Send on Behalf or Send As permission.

The default behavior can be changed by other outside factors:

• Administrators can update the from user's mailbox to always save a copy of messages sent from a delegate to their Sent Items.
• By setting the saveToSentItems property to false in a send mail request, you can prevent the item from being saved to the Sent Items folder. However, if an administrator has configured the "always save a copy" setting, the message will still be saved to the from user's Sent Items.

Examples

Example 1: Successful send through /me endpoint

In this example, Adele Vance has been granted Send on Behalf permission to Allan Deyoung's mailbox.

Request

POST /me/sendmail
Content-Type: application/json

{
  "message": {
    "subject": "Expense reports",
    "body": {
      "contentType": "text",
      "content": "Have you submitted your expense reports yet?"
    },
    "toRecipients": [
      {
        "emailAddress": {
          "address": "[email protected]"
        }
      }
    ],
    "from": {
      "emailAddress": {
        "address": "[email protected]"
      }
    }
  }
}

Response

HTTP/1.1 202 Accepted

Example 2: Unsuccessful attempt to send without permissions

In this example, Adele Vance attempts to send an email from Patti Fernandez, but has not been granted either the Send on Behalf or Send As permission. The response contains a ErrorSendAsDenied error.

Request

POST /me/sendmail
Content-Type: application/json

{
  "message": {
    "subject": "Support ticket",
    "body": {
      "contentType": "text",
      "content": "I noticed you opened a support ticket yesterday..."
    },
    "toRecipients": [
      {
        "emailAddress": {
          "address": "[email protected]"
        }
      }
    ],
    "from": {
      "emailAddress": {
        "address": "[email protected]"
      }
    }
  }
}

Response

HTTP/1.1 403 Forbidden
Content-Type: application/json

{
  "error": {
    "code": "ErrorSendAsDenied",
    "message": "The user account which was used to submit this request does not have the right to send mail on behalf of the specified sending account. Cannot submit message.",
    "innerError": {
      "request-id": "24e7991e-01ae-4cc2-8e06-532a96fd8948",
      "date": "2019-01-16T18:53:25"
    }
  }
}

Next steps

• Why integrate with Outlook mail
• Use the mail API and its use cases in Microsoft Graph v1.0