Why is Gmail blocking CSS in emails?

Question

I used CSS in my email and sent it out.

When I received the email in Gmail, all the CSS was disabled; however, when I retrieved the email in thunderbird or outlook,

Answer 1

I am answering it too late but this may help someone here. To be able to view your mail as it is in gmail and other email clients, you need inline style for each tag in your html, but writing inline css for each html tag is time consuming, to save your time use the builtin tool

http://templates.mailchimp.com/resources/inline-css/

Just paste your whole email template and you will get the html document with inline css in each tag. That much easy :)

Note: you can have your class and id in class as it is.