The default style of conversations we implemented is inspired by Gmail, so the order is currently only from the Oldest at the top to the Newest at the bottom. The messages marked as read will be collapsed by default so you will always be able to read the newest messages comfortably, but if you want to read the whole thread you can do so in a natural order.

In eM Client 10, the option to reverse the order of conversations was added. You can find this option via menu > View > Conversations, or in menu > Settings > Mail > Conversations.