Knowledge of Computing...

Lookeen finds everything fast in Outlook — no matter the account, folder, PST file or type (from email to meeting to attachment).

Pros
Lookeen finds emails, contacts, appointments and everything else fast in Outlook
You can easily reach related emails from Lookeen search results
Lookeen supports advanced search operators (but does not help you much using them)

Cons
Lookeen's "back" button goes back to the last search string, not the last thing you've seen
Search strings could be interpreted more loosely, related message search more intelligent
Lookeen does not index new email and changes you make in real time
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Description
Lookeen finds messages, contacts, tasks, meetings, appointments and notes in Outlook.
Attached files of many a type (including Office documents and PDF files) are found by Lookeen, too.
In addition to keyword search, Lookeen returns conversations (based on contacts) and related messages (looking at subjects).
You can configure PST files, folders and attachment file types to search. Lookeen supports Exchange, POP, IMAP and Hotmail.
Lookeen updates its database on a schedule (anything from every few seconds to every few days), and can pause during work.
From Lookeen search results, you can open, move, delete or categorize emails easily.
A bunch of messages can be summarized, say for forwarding.
Operators let you restrict Lookeen searches to certain fields, or expand them with wild-card characters, for example.
Lookeen supports Windows 2000/XP/Vista and Outlook 2003/7.
Guide Review - Lookeen 1.0 - Outlook Search Add-On

If it's there, Lookeen will find it. "It" can be anything from an email message to a contact, task, attachment or appointment. "There" can be in any Outlook PST file and any account type — from Exchange to POP, IMAP or Hotmail.
Lookeen not only finds, of course, it also finds fast; faster, it seems, than Outlook's built-in index search. With the results found and displayed in a nice separate window, Lookeen can perform a number of stunts, too: show only a certain type (only emails, say, or just meetings), only time range, find related messages by subject or contact, and operate on emails. Swiftly can you move, copy, delete or, of course, open emails, for example.
If a simple keyword search did not get you the sought result, Lookeen lets you employ search operators that find phrases, for example, or look only in the "Subject:". Lookeen lacks an interface that would construct such queries for you, though, and sometimes you wish the simple search were more forgiving — and include inflections or alternate spellings.
Behind Lookeen's fast results is an index of all data. When you first install Lookeen, that collection has to be built from the ground up, which can take a while. Subsequently, new data is added quickly on a schedule. You can choose an interval from a few seconds to days. Listening to what Outlook does and having new emails or changes you make in Lookeen instantly would be even better, of course.