Using conditional comments you can target different versions of the email outlook client and include your client specific HTML.
HTML Email Knowledge Base
List of Gmail supported CSS Properties & Media Queries
A list of all CSS properties supported in Gmail and Inbox.
Remove gaps between tables in Outlook 2007 and 2010
Outlook 2007 and 2010 can be a little tricky when it comes to stacking tables side by side or top to bottom, where you may see some undesired gaps between your tables.
Outlook 2007 – 2013 ignores margin and padding on images
Outlook 2007 – 2013 ignores margin and padding CSS styling when placed within an image.
Gmail clips emails exceeding a file size of 102KB
If your email exceeds 102KB in file size, Gmail will display the first 102KB along with the the message “[Message clipped] View entire message”.
