Roundcube needs as every good mail client does a search feature.
The user should be able to search for user-specified criteria in user-specified (sub)folders.
The request can take a few secounds, but if you have more than 1 folder, it is annoying to select each folder one by one and re-type your search string every time.
Cheers, Till
http://trac.roundcube.net/ticket/1485234
List info: http://lists.roundcube.net/dev/