ANSWER:

If kmail fails to send e-mail it will save it in Local Folders “outbox”, not the IMAP outbox. Same thing with sending e-mail, if there’s a problem with writing to default sent-mail it will save it in Local Folders.

All in all, inbox, trash, drafts and templates are useless. Outbox and sent-mail are not.

I’d suggest keeping them. Of course you can always redirect in your profile where Inbox, Outbox, Trash, Drafts, etc. should be, but Local Folders remain as a fallback.

by Hubert Kario from http://unix.stackexchange.com/questions/39454