We are working on a website that turns out differently from what was intended when Outlook is running.

When outlook is not running, all css seems to get loaded (the website looks great). When outlook is running, the website's css is not completely executed (or at least it does not show). For instance, background-colors of some elements are shown, of other elements are not shown.

Atm we are rewriting the css files as well as removing the inline style elements (so it might be cache-related?)

Multiple css-files are linked within the head-tag.

Hope someone can tell us where to start searching for a solution.