Reindex Messages

If Unibox doesn't display all results when searching for message contents, it might be necessary to reindex the messages manually. To do so open the Terminal.app and enter:

mdimport ~/Library/Containers/com.eightloops.Unibox/Data/Library/Application\ Support/Unibox/Spotlight

Since this will update the spotlight index of all your message files it might take some time to execute.