I am using a Litmus responsive email template for the first time and it appears that it is stretching my header image vertically. The image is enlarged for Retina at 800px by 1200px but reduced to 400px by 600px using HTML (width and height within image tag). It looks fine on mobile clients, but is stretching the image vertically on Outlook 2007, 2010, 2013, 2016 and Gmail on Firefox, Chrome, Explorer, and Google Apps on Chrome, Firefox, and Yahoo Mail on Explorer, Firefox, and Chrome.

Could anyone tell me why this might be happening and how to fix it?

Thank you!

Helen A