Add an existing shared mailbox to Outlook mobile app for iOS and Android

Use a shared or delegate mailbox on a mobile device (phone or tablet)

A shared mailbox is an email account that is shared amongst several persons.
A delegate mailbox is an individuals own NSCC account that they have given you access to.

To access a shared mailbox on a mobile device, use the following steps:

First be sure to have the Outlook Mobile app already setup with your own NSCC email account.

See the related Articles listing on the right side of the page for more information on that.

Tap '+Add Mail Account', then tap 'Add a shared mailbox'. 

 

Type in the email address of the shared or delegate mailbox that you were given permission to. 

After the account setup process completes, the shared mailbox will display in your account list in Outlook for iOS or Outlook for Android. 

To remove a shared mailbox, go to Settings > Accounts. Then tap on the shared mailbox and select Delete Account. 

More details:
https://support.microsoft.com/en-gb/office/add-a-shared-mailbox-to-outlook-mobile-f866242c-81b2-472e-8776-6c49c5473c9f