If the image you have uploaded into your activity is more than 1728px, Outlook 2007, 2010 and 2013 will crop it.

These versions of Outlook are using the Word 2007 rendering engine and these mail clients will crop the upper portion of all images higher than 1728 px. Other email clients and other versions of Outlook will not crop the image, however to avoid this in Outlook 2007, 2010 and 2013 you should do one of the following:

1. Use images less than 1728px high. We would recommend no more than 1700px.
2. Split the image into two separate images and upload as two different banners.