For which css features are implemented in each email client <a href="https:&#x2F;&#x2F;www.campaignmonitor.com&#x2F;css&#x2F;" rel="nofollow">https:&#x2F;&#x2F;www.campaignmonitor.com&#x2F;css&#x2F;</a> . 
It is a really good resource when creating email html templates and you are dealing with odd css quirks.