Theirry, I’m not absolutely clear what your question is - not exactly certain. I think there may be a typo.
Ghost doesn’t automatically create a page published on your website that is a copy of (or similar to) each email newsletter sent out. So, there is no ‘out of the box’ URL for each email newsletter to social share, either manually or automatically by, for example, a social button.
However, there is a manual option you can set up with a bit of ‘coding’ that can be used to keep your newsletters as pages on your site. It may not be exactly what you want, but perhaps it will do. You could keep your newsletters as ‘Collections’ on your site and those pages can each be socially shared. If that’s what you’re interested in, then this article explains how to do that. As you’ll see, it’s not something that can be toggled in the back end. It would be possible to code a social link button for each collection and it would obviously be possible to simply manually share the URL for each newsletter in the ‘Collection’ once you had set that up as per that article.
BTW, ‘Collections’ are not quite the same as ‘Tags’ and the difference is quite confusing at first for those who arrive at Ghost. Especially if they are comfortable with the WP methods of compartmentalising posts and pages. Lots of info in the help pages here about that too.