In TalkTalk Mail I use Vertical as the Layout option that means I have 3 vertical panels, Folder View on the left, List View in the middle and Email Detail view on the right.
I can recover more horizontal space by toggling the Folder view to icons only and, to list more messages in the List view vertical space, untick the Show text preview in Settings, All Settings, Mail, Message List.
I hope that's helpful.
