Link to all posts page?

Your 2nd example omits the leading / in the URL — does /wp-admin/edit.php work?

Also, you’re wiser to use admin_url(), since it’s possible to change the Admin URL to something other than /wp-admin. Instead of <a href="https://wordpress.stackexchange.com/wp-admin/edit.php">, use <a href="https://wordpress.stackexchange.com/questions/103685/<?php echo( admin_url("edit.php' ) ); ?>">. It’s more complicated, but much safer.