Hi ICS_YZ,
I understand you have created shared mailbox and set delegate(full access permission). This mean delegate can view/edit shared mailbox’s calendar in OWA and Outlook client automatically. In Outlook 2007, you will see the shared mailbox attached to the delegate mailbox and delegate can update the calendar of shared mailbox as below screenshot.
Regarding Email address shows G2de856a1ab4e416faa45ac2c96323ce9@mydomain.com, this is not expected behavior. Sometimes it is related to server side. So, we need to delete it and re-create it to check the issue via PowerShell or Exchange admin center.
If you would like to grant all users access to the calendar(For example, ), please run the following cmdlets to achieve the goal.
Add-MailboxFolderPermission -Identity share@domain.com:\calendar -AccessRights LimitedDetails -User default
Thanks,
Johnny Zhang