class Mail::IMAP

def delete_all(mailbox='INBOX')
  mailbox ||= 'INBOX'
  mailbox = Net::IMAP.encode_utf7(mailbox)
  start do |imap|
    imap.select(mailbox)
    imap.uid_search(['ALL']).each do |uid|
      imap.uid_store(uid, "+FLAGS", [Net::IMAP::DELETED])
    end
    imap.expunge
  end
end