Excluding Site Mailboxes from People Picker autosuggestions
When for example sharing content or assigning permissions as an end user you use a people picker that has an autosuggest feature, showing suggestions in a dropdown as you type. This autosuggest feature looks up objects from the active directory without any filtering and there is no way to configure this. So if you for example you enable the site mailbox feature, this creates an object in active directory that is not a user and not a security group. This is not an object that you would like to be presented in the people picker. An option to configure this would be good to have, or just to exclude all non-security groups by default.