How to implement a messaging system?

Dear list

(I guess this follows on from my previous posts...)

I'm trying to set up a simple messaging system using Magma, to enable users to pass messages to one another. I considered creating a 'mailbox' Collection for each user, in which messages could be stored, and which could be polled at regular intervals to check for new messages.

However, since each session has its own view of this object, any other user/session dropping a message into the Collection would violate the rule 'do not share objects between MagmaSession instances'.

What is the proper way to implement such a system? I'd be very grateful for any insight!

Amir