Client posed this question.. not certain how to answer it. Assuming multiple mailboxes reside within the same mailbox database. If an attachment is addressed to each in a single thread, does the attachment size reflect against the mailbox size for each recipient? If so, isnt this technically incorrect? If not, then to which mailbox does the attachment size post?

I believe the individual mailbox reports, all added together will be larger than your actual database because of this situation. SIS is working, but individual user reports do not reflect this "under the hood" technology.

So it is your belief that each mailbox will reflect the space required by the attachment, regardless of whether the attachment is actually stored once per database? I have tested this, but get odd size reports. There does appear to be some growth per mailbox when sending attachements, but the database size growth doesn't add up. Must be due to compression or manipulation of the attachment data type when committed to the database iteself. Thanks for your response.