Kenny Zaron

This plugin allows for network administrators on WordPress multisite environments to send an email to users that 
they select based on the users’ roles in individual sites. For example, checking only “editors” will go through 
each active site and add anyone with the role of “editor” to your list of emails to send to.
To use the plugin after installation & activation, find Users / Mass Email in the network admin dashboard in your 
multisite install. Then, select the user types you wish to email and click on the button for “Load the List”. This 
will load the list of users to email. Then you may compose your email in the boxes provided and click the send 
button at the bottom of the screen. If all goes well you will be presented with a confirmation page indicating 
that your email was sent successfully.
This plugin is NOT intended for administrators to be sending unsolicited spam to their users. In fact, it was 
created with more formal environments in mind. One example would be a University setting where administrators 
of the network may need to notify students and faculty of potential downtime. With the plugin’s implementation 
I would imagine it would be a highly inefficient way of sending spam anyway.

Network Mass Email

Allows network admins to send a manually created notification email to all registered users based on user role.

Sybre Waaijer

Pro Mime Types adds a nifty (network) admin interface for allowing or blocking many file extensions for uploading media, documents, and other attachments.
It also shows you a list of all allowed MIME types on the site or network.
<ul>
<li>When a MIME type is allowed, users who can upload files can now do so for that MIME type.</li>
<li>When a MIME type is blocked, users see an error that the file isn’t allowed for security reasons.</li>
</ul>
For WordPress Multisite networks, you can enable this plugin in network mode to control MIME types for the entire network.
<h3>Features</h3>
<ul>
<li>You can control many MIME types and extensions for upload via a modern interface.</li>
<li>Pro Mime Types comes preconfigured by enabling many safe MIME types.</li>
<li>View all allowed MIME types for the site (also those enabled by other plugins).</li>
<li>Every MIME type comes with a security summary explaining why you should or shouldn’t allow it. To view the summary, hover the mouse cursor over the big colored icon.</li>
<li>Accessibility is at the forefront. For example, you can use full keyboard navigation, even for tooltips.</li>
<li>Adds text, code, and miscellaneous file types to the Media Library for sorting.</li>
<li>The Media Library gains support for more file types for sorting images, audio, video, documents, spreadsheets, and archives.</li>
</ul>
<h3>Multisite support</h3>
This plugin can run in network mode, where all sites are allowed one set of MIME types. You can configure the allowed MIME types via the network administration UI.
Alternatively, Pro Mime Types can run in single-site mode, where every subsite has custom-allowed MIME types. Only the network administrator can assign these on a per-site basis.

Pro Mime Types – Manage file media types

Pro Mime Types adds a nifty admin interface for allowing or blocking many file extensions for uploading media, documents, and other attachments.

Network Mass Email vs Pro Mime Types – Manage file media types