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: 
No.

You can't apply pesudo-classes (or anything else that appears in a selector) via the style attribute.
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.