Question: The question is to know if there is a way to build an HTML email with inline style (no CSS file, nor `<style>` tags) with the href links that react with the mouse passing over them : just to be able to change the color font.

So, no JS, no script, no `<style>`, just `<a href="http://www.dot.com style="....">link</a>`

Answer: 
Some E-Mail clients support `style` tags, and thus the defining of pseudo-selectors. According to this list:

[Guide to CSS support in E-Mail clients](http://www.campaignmonitor.com/css/)

`:hover` is supported by a good number of clients.

You should be able to slip a `<style>` tag into the body if necessary. That's not valid, but rich E-Mails are such a minefield that that is going to hardly matter.

`:hover` is your only chance I think. It's not possible to define pseudo-selectors inline, and JavaScript is out because it's going to be blocked by most (or all?) clients.
You can, however, you will not be able to change the color of the underline. You can wrap the the link text in a div and then wrap the div in a link, like this:

```
<a href="http://www.google.com"><div style="margin: 0px;padding: 20px 50px;font-size: 50px; color: red;">GOOGLE</div></a>

```

The word "GOOGLE" will appear red, but with a blue underline. So that does not exactly solve your problem, I don't think.