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How Exchange 2003SP2 handles attachments to from one user to multiple users.

rhowell3 asked
Last Modified: 2010-03-06
We are running Exchange Enterprise. 2003 w/SP2.  If a user from inside the domain sends a 1meg file to 10 users in the same domain, how is the space accounted for in Exchange?  Will the total space on the Exchange Server be 1meg and a pointer sent to the users, or will the Exchange Server see it as 10megs.  (One Meg per each user's mail box)

Same question, but what if the sender is outside the domain sending a 1meg file to 10 users in the same domain?  Will the Exchange Server see it at 1meg per user's mail box, or will it use some type of pointer? Any help is appreciated.
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Exchange utilizes what Microsoft terms a single-instance message store. This single-instance message store works on a per database basis. What does this mean? If an e-mail message is sent to multiple mailboxes that are all in the same database, the message is stored once and each mailbox has a pointer to the message. The transaction is also logged in the transaction logs for the Storage Group that contains the database. However, if the e-mail message is sent to multiple mailboxes that are located in different databases, the message is copied to each database and written to the transaction logs for each Storage Group that contains the database with a copy of the message.

For example, if I send 10 users a 1MB email message and all the mailboxes are located in the same database, one copy of the message is written to the database and each mailbox points to this message which will consume 1MB of disk space in total. If the 10 recipients are located in two different databases, each database will get a copy of this message which will consume 2MB of disk space. As you can see this is a much more efficient use of space as opposed to the alternative of 10 1MB messages using up 10 MB of disk space.

Forgot to mention that if you move the mailbox or migrate from the server the single instance is lost and the attachmant is copied to each users mailbox


Thanks for the quick reply.  I was under the impressiong that was the way it worked, but I wasn't sure if it only worked that way with internal e-mail ver. external e-mail.  Thanks again.
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