Shared mailbox on Office 365 can be very useful and served as many roles. When granted with full mailbox permission, the mailbox can be automatically shown up in your Outlook without extra configuration. There used to be a setting in Office 365 admin portal that can turn this auto-mapping feature on or off but I don’t seem to be able to find it anymore.
So, here comes PowerShell again.
First of all, open a new PS session to the Office 365 tenant.
$userCredential = Get-Credential $Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://outlook.office365.com/powershell-liveid/ -Credential $UserCredential -Authentication Basic -AllowRedirection Import-PSSession $session
Then, use Add-MaiboxPermission cmdlet to grant permission with the Auto-Mapping switch.
Add-MailboxPermission -Identity emailaddress -User emailaddress -AccessRights FullAccess -AutoMapping:$true
Replacing -AutoMapping:$true with -AutoMapping:$false will turn the Auto-Mapping off in Outlook.