Why does the order of incoming mail at the bottom view…put the mail oldest to newest, in other words the newest email in a sequence is last.
Postbox put this is an order where the NEWEST email of a sequence is at the top. I stopped using this program some time ago & decided to use it for one name, then I disovover this,
Can it be changed or modified?
Click on the newest or oldest and it will change the order.
do not see a newest to click on. they are in order on the TOP pane, not the BOTTOM pane. 
I see what you are asking. You are talking about the conversations listed in the message detail, not the emails in the message list. My mistake. You cannot change this.
I actually raised the same question. https://forum.emclient.com/emclient/topics/order-of-messages-in-conversations