GreenAnt Email supports advanced search options using IMAP Full Text Search. This means that your email is indexed on the server to allow faster searches. Unfortunately, not all mail clients support these standards.
The following is a guide to search methods when you need to search many folders and thousands of messages.
OS X Mail
Web based solutions
GreenAnt supports an alternative web based search interface with a full-text search option. It can be found at this link. We are working on integrating multi-folder search into the current webmail client.