Option 1: Searches on a mailbox-by-mailbox basis
If you're just looking to perform content-level searches on a mailbox-by-mailbox basis, I strongly recommend that you look at a solution that Microsoft recently acquired called Lookout. You can get this tool here. Lookout will index all e-mail content in your mailbox, across any number of PSTs, and files throughout your local and network file systems in order to provide virtually instant search ability across all your data.
Option 2: Global searches
If you're looking to search across an entire infrastructure for individual keywords or strings, then you are definitely faced with quite a challenge. For starters, there are four key areas you need to keep in mind, especially if your search is part of a legal investigation or for compliance purposes. You'll need to search within each of these locations:
-- Within your online storage: Essentially, you'll need to have functionality to initiate search(es) across all Exchange stores in any storage group and on any server in your environment. Doing this well is difficult and there are only one or two vendors on the market who have solutions to achieve this. If you can get away with simply searching for strings/keywords in subject lines only, then there are a number of vendors who provide solutions enabling this.
-- Within your backups: Obviously backup tapes hold a copy of all mail at a given point in time. Finding a solution that allows you to search within your databases -- while they are offline or still on tape -- for keywords in either messages, or even within attachments, gives you the flexibility you need to find whatever you're looking for across all tapes. There are two vendors with solutions in this space, only one of which enables search within attachments.
--Within your archives: If you have an archival solution in place, then the vendor who sold you the archive has likely provided you with the ability to search message content for what's in your archive.
-- Within your file system (i.e., PSTs): Finally, you'll need to make sure you have a good handle on PSTs, especially if you're being asked to find all messages anywhere containing specific keywords or strings. Again, there are few vendors with solutions in this space, but the ideal approach would be a combination of (i) locking down PST creation abilities and then controlling this carefully, and (ii) auto-detecting all PSTs of interest and dumping their content back into Exchange where it can be managed.
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