In our 2.0 API, we keep an index of email headers so that the list message resource can be filtered by a few of the same parameters that gmail's search box supports. You can see the list of params here: https://context.io/docs/2.0/accounts/messages#get
We don't currently index email bodies or the contents of attachments. If you want to do a search on the bodies, you'll have to iterate through the messages and either perform the search, or index metadata so you can recall it later. If you go that route, then I recommend using the `include_body` optional parameter, so that the message body is returned in the list message call.
If there's a specific kind of email search you're looking to do, let me know and I can help guide you on how to do that with Context.IO.