Narrow Message Display

Having got a new laptop with HD screen, I find that Outlook 2013/2016 doesn’t display newsletter type emails correctly. They are displayed in a narrow column centrally in the message pane with wide space either side. So I am trialing eM Client and Thunderbird as an alternative. Thunderbird displays all message correctly but has other issues which I won’t go into. eM seems to fit my requirements well in most cases and the emails in question are displayed correctly. But some other emails are displayed in larger font resulting in fewer words per line compared to Outlook or Thunderbird.

Zoom out does not alter the words per line and changing the font size in the settings for READ has no effect, as this setting apples only to plain text email while the mail in question is HTML format. Are there any settings I am not aware of that would change my message pane?

I’ve attached a comparison of the email message. I like all other aspects of eM, but could be a decider for me if I can’t fix it.