How can I send e-mails in HTML+CSS format so that CSS is applied?
After some tests, I've checked that whereas CSS works in Outlook, it apparently doesn't work in Gmail. By the way the CSS propoerties are located in the same and only HTML document.
Which CSS attributes are you trying to use? A lot of online mail services turn this stuff off by default unless the user marks them as from a trusted user so it's a good idea to have something that looks okay with and without.