Thunderbird is an all around decent enough mail client. I have about 10 email accounts that I use regularly and I manage it all with Thunderbird. The search feature is nice when you want to search within an email account, as it changes the contents of your inbox on the fly based on your search terms. A more advanced find messages tool allows you to put in multiple search strings and perform basic logic. You can even create a folder full of saved searches - pretty handy indeed.

Where Thunderbird falls short is the ability to search across multiple accounts. I need this feature at least once a day and always end up banging my head against a wall trying to figure out which account I used for a particular email I am trying to find. It's completely maddening. I cannot figure out why they would not include such on obvious feature or if I'm just too dumb to figure out how to use it.

The one workaround I have found is to create a saved search folder that searches all available accounts. The drawback is you need to edit the search folder every time you want to perform a search. Annoying, yes.