Typical issues for Outlook
Outlook is also a very popular email software but there are some problems that you might encounter when it displays your emails. Typical issues have to do with borders around images, background images, margins and paddings. By default, Outlook appears to attach borders to all images and thus, you need to add the style “border:none;display:block” to every image that you don't want border around. When it comes to background images, some versions of Outlook don't usually display them and thus the solution is to add Microsoft VML code before the content and close it after that.
Within the VML code, there are several important details: you need to define exactly where the background image can be found, you need to define the height and the width in two separate places within the VML code and they both have to match the height and the width of the table data cell and the image that is being used as a background. This approach will definitely display background image in Outlook and Outlook.
Another issue that you might find with Outlook has to do with floats and margins vs paddings. When you code an HTML email, it is never a good idea to use floats. Instead, at the table data cell level, you should use the valign and the align to define where data floats are positioned. In addition, you should know that Outlook is more likely to respond to margin setting than it is to respond to paddings so you can simply switch padding to margins and see if that works.