One of the most popular email complaints I receive are about unwanted horizontal gaps in newsletters. These gaps are normally ill-placed in the middle of a paragraph or between a paragraph and an image; making your newsletter just look wrong.
A common denominator between these emails is they have all been viewed in Outlook 2007, 2010, or 2013. As for some reason, the email community can't fathom, Microsoft stopped using Internet Explorer to view emails in Outlook and began using Microsoft Word as their rendering engine since Outlook 2007. However, this excludes Outlook 2011 and 2015 as they are on a MAC.
You might not think viewing your email in Word would cause problems, but it does. This is due to a word processor interpreting the HTML and trying to make some sort of sense of it for you which brings me to those gaps. These are actually similar to page breaks called 'text boundaries' used for printing. Which explains a lot!
The problem comes in when these text boundaries can only be a height of 23.7 inches (approximately 1,790px for those pixel people). And when that height is maxed out, your email is broken up to fit into these confines. Here is what an email looks like with the gap and without the gap.
What can you do to fix this? The first thing I always do is see if I can move around those content areas. As there might not be a gap when the content is in a different order. And if you are not able to change the order, you can always add text or images above the area that is breaking.
Then there are the code fixes; adding breaks or paragraph tags, force a page break , add a height attribute to the broken td, or messing with your tables.
In the end, if you have pulled out all your hair, don't forget to contact the email marketing department. As we can speak Outlook and can assist you in taming the gap.
Thank you Email on Acid for providing great resources.