That once you give it your login crdentails for the remote e-mail service...
GMAIL will go and search look for folder and make labels for them and download and label all of them.
It worked great in 2009, just recently it worked really excellently for another company I migrated. The whole company migrated from another webmail/exchange service in about 3 days all 8M plus messages from the exchange service they were using was migrated.
They have saved over $3000/year and now have collaboration tools and pages and etc...