Fixed issue for Microsoft 365 Shared Mailboxes.

[MarcBanyard]

Fixed issue for Microsoft 365 Shared Mailboxes.

This issue has been discussed in the following forum post https://forum.osticket.com/d/101462-oauth2-shared-mailboxes/34

This push fixes and resolves the issue so that the resource_owner_email is set correctly as the Shared Mailbox email on the Remote Mailbox tab and the User Mailbox / Global Admin is set on the Outgoing (SMTP) tab.

The logic for this is

• To pickup emails you need to use the email address of the account that emails were sent to, this can either be a User Mailbox or a Shared Mailbox.
• To send emails a Licenced Microsoft 365 User Mailbox must be used, so the emails are sent from the User Mailbox account that is used to authenticate the Shared Mailbox or the actual User Mailbox on the Microsoft 365 OAuth2 challenge.

If using Shared Mailboxes, the User Mailbox account that is used to send emails is often referred to as a Service Account or a Global Admin account. This account needs to have permissions to be able to access and send emails on behalf of the Shared Mailbox(es) that you configure on your osTicket configuration.

[MarcBanyard]

This Pull Request contains the required fixes from Merge Request #254 which has been extended to fix the issue many users were reporting on the forums when it comes to sending emails from a Shared Mailbox.

Emails need to be sent from a Licenced Microsoft 365 mailbox which is a User Mailbox as a Shared Mailbox can't have a Microsoft 365 licence assigned to it.

[protich]

@MarcBanyard - Thank you for the pull and the detailed explanation. I've added to your commit, please see #265