Corporate data is typically spread across a lot of locations – document repositories & file systems, collaboration/project data, RDBMS, Email etc. This makes a good email search tool important.
However, unless your users are particularly well-trained at dealing with email, most of the mail they receive will remain in their mail file or archives – accessible only to them (& maybe their assistants), and generally out of reach of other users.
That’s OK, because mail is a personal data store, in that if you received the mail, you’re allowed to know about it – other users might also have received the mail, but only if they’re allowed to know about it too.
Users often categorise mail into folders, or make lists of the most important emails, but generally it’ll be a vertical well of information, sorted by date, and probably with one or more archives for the really old stuff.
Over time, finding such information becomes more and more difficult – because users need to know roughly where it is. If they forget that, it can take a long time to find, or just not be found at all. It’s surprising how much time (and therefore money) is spent looking for information “I know is there somewhere”.
A comprehensive mail search facility is essential to ensure that each user can efficiently use the data that they & only they have – in their email database. And for real efficiency, users need be able to search that data at the same time as public data, and in its entirety (not by opening each mail file/archive and searching separately).
Outside of implementing a policy/procedure whereby all mail is managed, e.g. moved to another location (which is usually fairly ambitious as users have neither the time nor inclination), adding an email search tool is the most effective way to make better use of your existing IT environment, without limiting you from implementing & receiving the benefits of newer, more social technologies.