For my corporate email I use Microsoft Outlook against the corporate Exchange Server. I organize my email using categories, rather than folders - and use search folders to locate email. Some of the categories are assigned automatically depending on where the email comes from or keywords in the subject line (or a combination of these). This works quite well in the corporate environment - however I myself use other environments too including Android. I notice that using categories in fact write the categories into the email header like this:
I am wondering - are there other clients for Android that could read these categories - and search one them? I can access my email by IMAP too - so that ought to broaden the possibilities.