Wikipedia:Requests for permissions/Mass message sender/Administrator instructions

Mass message sender is a user group that allows users to send messages to multiple users at once.

Prerequisites
In general, mass message sender is only granted to trusted users who:
 * 1) Regularly requests mass mailings or otherwise have shown a need for it
 * 2) Have filed at least one request for mass message delivery clearly showing an understanding of the guidance for use

An overview of the guidance for use:
 * 1) Don't spam or canvass users
 * 2) Messages should only be sent to users who are likely to want their attention drawn to the message
 * 3) If it's a regular newsletter, make sure you include a way to unsubscribe
 * 4) Don't send out paragraphs of text or flashy imagery bloating talk pages. Keep it concise and to the point, but also feel free to spice it up with some formatting

If they've been manually going talk page to talk page over and over, this is essentially the same as requesting a mass mailing and should provide enough evidence to determine if they can be trusted not to misuse the tool.

In short, you'll probably only end up granting this right to event or WikiProject coordinators -- just make sure they know how to properly construct a newsletter.