Here’s how to add a Microsoft Office 365 shared mailbox on the native Mail app of an Apple iOS device.

Native iOS Mail App instructions:

1. Go to Settings > Mail, Contacts and Calendars > Add Account.
2. From the choices available, touch Other near the bottom.
3. On the Other screen, touch Add Mail Account.
4. In the new screen, you will enter:
   • Name: The name that will be displayed to recipients on email.
   • Email: The email address of the shared mailbox (e.g., mailboxname@company.com).
   • Password: Your own Office 365 password.
   • Description: Your chosen description.
5. Touch Next to get to the full settings.
6. On the following screen, confirm that IMAP is selected at the top.
7. Scroll down. In the Incoming Mail Server section, enter the following values:
   • Host Name: outlook.office365.com
   • User Name: Your personal email address, followed by a forward slash, followed by the name of the shared mailbox. For example, your.name@company.com/mailbox
   • Password: Your own Office 365 password.
8. Scroll down. In the Outgoing Mail Serversection, enter the following values:
   • Host Name: smtp.office365.com
   • User Name: Your Office 365 email address.
   • Password: Your Office 365 password.
9. Touch the Next button and wait for the server to verify your settings.
10. Choose your synchronization choices and touch Save in the upper right corner. You will now find the shared account in your Mail app under Mailboxes.