How to access Office 365 Shared Mailbox (Calendar) on iOS

Client has Office 365 E3. Has a handful of users. They have a Shared Mailbox where they all access and use the Calendar.

Now, they need to be able to access that Shared Mailbox Calendar on iOS. I'm aware that MS does not want people to do this but there is a workaround:

1. Add Account
2. Other
3. Add Mail Account
4. Name: Name of shared mailbox
5. Email: email address of shared mailbox
6. Password: of user who has full access to shared mailbox
7. Description: Name of the shared mailbox
8. NEXT
9. IMAP
10. Incoming Mail Server: outlook.office365.com
11. Username: (your_primary_account)@domain\enter_the_name_of_the_shared_mailbox
12. Password: of user who has full access to shared mailbox
13. Outgoing Mail Server
14. SMTP: smtp.office365.com
15. Username: email address of the person who has full access to the shared mailbox
16. Password: of user who has full access to shared mailbox

I can confirm this works fine as I have just added a Shared Mailbox from my own Tenant onto my iPhone.

However, once the account is Verified the only mailbox items I can sync are:

• Mail
• Notes

No Calendar :-(

Besides converting the Shared Mailbox to a full mailbox, is there any other way?

Thanks
Mark