When you first visit the mail overview (messages url), you can see that the coversation boxes are about 10px away from their right border. It also happens if you switch between multiple coversations/mails. If you hover over the box, it jumps into it's correct positon.
I tryed a few things, but wasn't able to solve it. I guess there's some kind of javascript or anything else interfering with the container. The contaner should be "#conversationItemListSub".
I was able to reproduce that kind of behavior on your demo. Just send two mails to two different users, then visit the message-page and click through the both conversations.
I know, it's not a big deal, but it's just annoying. I am using Chrome, and it looks like, that this doesn't happen on Edge, Vivaldi and Firefox. So it seems to be a problem of Chrome only.
Best regards!
Edit: Btw - You're having the same ~10px margin/passind on the message history (.ow_mailbox_right) as well. On first init.
