Question re Single Instance Storage of emails

I understand that GroupWise stores a message sent to multiple users only once within the PO and does its magic with pointers, etc but does it do the same if a user in one post office sends an email to multiple users in another post office. If so, will this work across post offices that sit within separate GroupWise domains but in the same system? And finally if this is still the case, will it do the same for an email sent from the internet to a number of users within the same post office?

Cheers,
Dave