How to code with Email Marketing?

I'm starting with Email Marketing, I've never done it before and I'm facing a world of difficulties. From the tutorials seen on the internet, I was able to draw the following conclusions:

• we use table so that it has a greater abrângencia and thus has no break layout.
• we use class style with [], because it is more conventional * ex: tr[class="foo"]{}
• we use inline styles style="" because email tools don't understand the tag <style></style>
• the web has evolved a lot, but the way to code for email marketing is still well out of date

If all of the above is right, I have some questions regarding responsive email marketing:

1) trying to send a responsive email marketing template that I downloaded on the net works from a tool I used called PutsMail , but when I try via GMAIL directly called Gmail append HTML , it does not get responsive. Why? What is the difference between the two?

2) How does Media Queries work when the style is inline? As far as I know there is no way to put media queries in inline style

3) in several email marketing tutorials, the instructor puts <meta name="viewport" content="width=device-width, initial-scale=1.0"> in the head, if it's all inline, how is the meta tag inserted just for viewing the layout? in the end, who will send is the meta tag of the site in which the end user accesses, right?

Thank you!