Adding a shared mailbox to Thunderbird - Instructions for M365 Shared Mailboxes

Note: To add a shared mailbox it is necessary to have all of the following:

  • A security group that grants “Send-as” and full access permissions to all folders of the shared mailbox (Your department IT support can help to have you added to a security group.)

  • Your account must be a member of the mailbox security group as your account requires permission to the shared mailbox for authentication using your own credentials.

  • Permissions on Windows Nexus computers become effective the next time you log onto the machine after the mailbox permission change has been made. You may need to sign out from your Nexus account on the machine and then sign back in again before you will be able to add the account and access the mailbox.

Contact IST Service Desk if your account does not meet the above requirements. IST Service Desk's contact information can be found at the bottom of this page.

Thunderbird is not the most suitable email program for Exchange. We do recommend using Microsoft Outlook.

  1. Go to Tools - Account Settings - Account Actions - Add Mail Account.

  2. Enter the following in the screen that follows :

    • Your name: Use exact name of the shared mailbox (e.g. Firstname: Shared Lastname: Account)

    • Email address: email address of the shared mailbox Use the max 8-character username of the shared account and (e.g.

    • Password: Leave PASSWORD field blank

      • uncheck ‘Remember Password’

    • Click Configure Manually.


  3. In the Set Up Your Existing Email Address window, enter or select the following settings in the Incoming and Outgoing columns as shown, then click Re-set.

4. This will check the server and add the OAUTH2 option under Authentication. Change the entry to be OAUTH2. Note that some of the settings changed as a result of the last step.




5. Your settings will now look as below:

6. Click Done

This will create the basic connection – and now we have to EDIT our settings.

7. In Thunderbird right click on the Shared Email account and select Settings:

8. Towards the bottom of the screen for Outgoing Server (SMTP) Click on Edit SMTP server
(In this example, the Shared Mailbox is; and the primary user is )

9. Change the User Name to be your own 8 character UWaterloo username – in this example: Click OK

10. Close and reopen Thunderbird. You will be prompted for the password for the Shared account you added. In this example the account is Enter an invalid Password and click Sign in

11. You will get a new login prompt that lets you change the username.

12. Enter your own username – in this example the username is Click Next.

13. Complete the login process by entering your own password and responding to the 2FA prompt.

Need help?

Contact the IST Service Desk online or 519-888-4567 ext. 44357.