One of the best utilities ever created for Exchange is EXMerge. You can get the latest version of this tool here, where it is listed as the Mailbox Merge Wizard: http://www.microsoft.com/exchan...
Updated Jul 01, 2019
Version 2.0
Blog Post
EXMerge does not preserve single instance storage, and it therefore causes a certain amount of growth in database file size. The reason that EXMerge can't preserve single instance is that it operates on each mailbox independently, without knowledge of what is in other mailboxes. EXMerge's duplicate detection is scoped to the level of a single mailbox, not the whole database.
How much will your database grow because of this? It varies widely, and depends on the mail habits of your users. More often than not, the single instance storage ration of an Exchange database is very low, approaching 1. The reason for this is that the "half life" of a message is inversely related to the number of people it is sent to (meaning, the more people a message is sent to, the more quickly people are likely to delete the message). This is explained briefly in this Microsoft KnowledgeBase article:
http://support.microsoft.com/?id=198673
As a rule of thumb, Microsoft PSS has recommended anticipating up to a doubling of database size after a full EXMerge of all user data.
How much will your database grow because of this? It varies widely, and depends on the mail habits of your users. More often than not, the single instance storage ration of an Exchange database is very low, approaching 1. The reason for this is that the "half life" of a message is inversely related to the number of people it is sent to (meaning, the more people a message is sent to, the more quickly people are likely to delete the message). This is explained briefly in this Microsoft KnowledgeBase article:
http://support.microsoft.com/?id=198673
As a rule of thumb, Microsoft PSS has recommended anticipating up to a doubling of database size after a full EXMerge of all user data.