Outlook 2015 for Mac: Resize email - line breaks

I'm using Outlook 15.4 (141114) for Mac on OSX 10.9.5

My problem is the browser view / viewing mails where automatic line breaks are set at the wrong point. It seems that the browser assumes a false display resolution or assumes the right end of the window to be far more right than it actually is.

In consequence all text is rendered with more width than the window actually has and the line breaks are calculated wrong.

Any hints how I could solve this myself?