The wonderful thing of the new X3 is the new webmail interface. It is now language aware, fully editable, themeable and feature management support. 3rd-party theme provider, now has more job to do. If you has ability to customize cPanel. You can do the same thing for webmail. It is also allow adding more logic on the webmail interface. I requested this for over 3 years, finally it happens.
One flaw on the X3 I found, it seems addon-modules are not fully support. I need to manually edit file /usr/local/cpanel/base/frontend/x3/cells/*.html to show the link to Fantastico and RVSiteBuilder. And my changes will be overwritten when cPanel update itself.
Heres how to do this:
# pwd
/usr/local/cpanel/base/frontend/x3/cells
# ls -l | grep ^d
drwxr-xr-x 3 root root 4096 Nov 6 07:41 advanced
drwxr-xr-x 3 root root 4096 Nov 6 07:48 db
drwxr-xr-x 3 root root 4096 Nov 6 07:41 domains
drwxr-xr-x 3 root root 4096 Nov 6 07:41 files
drwxr-xr-x 3 root root 4096 Nov 6 07:41 logs
drwxr-xr-x 3 root root 4096 Nov 6 07:41 mail
drwxr-xr-x 3 root root 4096 Nov 6 07:41 pref
drwxr-xr-x 3 root root 4096 Nov 6 07:41 sec
drwxr-xr-x 3 root root 4096 Nov 6 07:41 software
# echo '<div class="item">
> <a href="/3rdparty/MyAddon/index.php" target="_blank"><img alt="<cpanel langprint="IconFor">" border="0" src="<cpanel Branding="image(MyAddon)">" id="branding-img-MyAddon"></a><br />
> <a href="/3rdparty/MyAddon/index.php" target="_blank"><cpanel langprint="MyAddonn"></a>
> </div>' > software/myapp.html
Edit: this isnt' in EDGE yet