Harshit

Automatically subscribes your users so that they can be notified of any new content on the main site using one of the following plugins –
<ul>
<li><a href="https://premium.wpmudev.org/project/subscribe-by-email/" rel="nofollow ugc">WPMU’s Subscribe by Email plugin</a>.</li>
<li><a href="https://wordpress.org/plugins/email-subscribers/" rel="ugc">Email Subscribers & Newsletters</a>.</li>
</ul>
Note
<ul>
<li>In a multisite WordPress install, all the users creating new sites will automatically subscribed to the main site’s new content.</li>
<li>In a single WordPress installation, all users registering to the main site or getting added by other admins will be automatically subscribed to the main site’s new content.</li>
</ul>

Auto Subscribe Users

Helps us automatically subscribe all our new users being added to the multisite network in order send them notifications regarding new updates/important notifications regarding our service.



Works as described

Automatically subscribe your users, so that they can be notified of any new content on the site.

Emanuela Castorina

This plugin in a multisite installation shows the ID of the current site/blog in the admin bar menu. The ID of the current site/blog is linked to the site info page. 
It adds also a custom column with site id information inside the sites list table. 
It can be installed only on a multisite.

Wp Show Site ID

This plugin in a multisite installation shows the ID of the current site/blog.

Auto Subscribe Users vs Wp Show Site ID