def rename(mailbox, newname)
      send_command("RENAME", mailbox, newname)
    end
Sends a RENAME command to change the name of the +mailbox+ to
+newname+.

A Net::IMAP::NoResponseError is raised if a mailbox with the
name +mailbox+ cannot be renamed to +newname+ for whatever
reason; for instance, because +mailbox+ does not exist, or
because there is already a mailbox with the name +newname+.