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

Stylesheets are one of many, many HTML features that are often blocked by webmail providers.

HTML mail is a world of hurt and it's not going to get any better — in fact, you can expect it to get worse. Almost every feature of HTML is not supported in some mailer or webmail service. Anything at all modern is a dead loss. And of course there are still the text-only clients.

Unless you have endless spare time to burn uglying up your code and testing every last mailer, forget HTML mail. Just send a text mail with a link to a normal web page where you can be sure everything will work as expected.