Unusual format for message display

Just setting eM Clint up on my sister’s Mac and all messages display within a small browser window inside the message in either the preview pane or when opening the full message. I can double-click on the tiny browser window to open the message in a browser and that is fine but hardly a solution for all email messages. I have been using eM Client for years on my Windows PC with no such problem. Is this a Mac thing? It’s email like 1995 all over again.

In the first part of the displayed message there are all of these alerts about Send Read Receipts and Translation and that the message was not downloaded because I am not connected to the server and yet I am connected to the server as evidenced by the fact that the message arrived. So, I have disabled the AV (Avast was causing IMAP problems so I put in an exclusion and also disabled it for testing this problem) but no improvement.

Any ideas anyone?