Goal

1,000 contributors on MDN per month
Project goal: Increase participation and collaboration between contributors, leading to better retention of volunteers on MDN
Metric: # of contributors per month, % growth increases after messaging is launched
Metric: # of messages sent per month, messaging growth over time as correlates to contribution
Metric: % of contributors who continue editing after their first edit (over 3,6,12 months)

On-site messaging (direct, private communication among MDN users) will increase contribution and retention of contributors in several ways:

Increased engagement with newer users, encouraging them to continue to participate without having to install IRC clients or subscribe to mailing lists, as well as make sure they can find things to work on and are not facing obstacles to contributing
Contributors can form teams to collaborate on projects or articles
Leads of various areas can message others working on their topics or localization areas to help organize work, ask for help, etc.
l10n drivers can't contact editors who have left partially translated articles and work with them to get the articles completed.
Connect volunteer with others in their community (be that local, language-based, or topic)
Contributors can ask for reviews and feedback from peers, or volunteer to review or edit
Provides a secure way to interact on MDN without needing to expose your personal email address on the web.
Additional incentive to register, gaining access to other MDN services (profile, badges, etc.)

See SUMO's private messaging feature for an example of how this functionality might be implemented.

Also see the Social features page for related features that may affect design decisions, etc.

User stories

I want to send a message to another user who has given permission to receive messages.
I want other MDN users to be able to send me messages without exposing my email address on the Web.
I want to control whether other users can send me messages.
I want to control how I am notified about messages I receive (desktop notifications, email, on-MDN-boxes, twitter, etc).
I want to report and block a sender.
I want to reply to messages.
I want to archive, retrieve, and delete messages.
I want to send a review request to people who have expressed willingness to review articles about the topic my article is about, or (for editorial reviews) to people who have expressed willingness to do that.
I want to be able to report users who message me inappropriately.
I want to be able to send a message to all users working in the same topic.
I want to be able to send a message to all topic/l10n drivers for a given topic/locale.
I want to be able to send a message to all MDN admins.
I want to be able to subscribe to a topic/locale, so that I receive messages send globally to them.

I want to send messages to all members of my topic or locale "team".
I want to send messages to all other l10n/topic drivers.
I want members of my team to be able to message one another (or all team members) easily, to encourage my team to work together.
I want to subscribe to automatic summary messages about the l10n/topic I drive, so I don't have to click dozens of things all over the site to find this mission-critical information
- Digests of changes made
- Lists of pages with errors
- Lists of pages flagged for reviews or for translation work
- Etc.

I want to receive reports of abusive messaging behavior by users.
I want to appropriately handle reports about abusive messaging behavior by users. (Need to create a policy on how abuse will be handled. E.g., banning for obvious spam; otherwise, 3 strikes and you're out.)
I want to view messages that have been reported as abusive, so that I can take appropriate action on the sender.
I want to view messages sent to all topic members/l10n members/topic drivers/l10n drivers: we act as default l10n/topic drivers, inheriting all their capabilities.
I want to be able to create messages that are sent to all users (to announce downtime, major feature updates, surveys, etc).
(Maybe) I want to view any message as needed to maintain site performance and integrity (i.e., investigate suspicious activity).
I want to be able to create new topic groups.

On-site notification of new messages
On-site reading of messages
On-site replying to and deletion of messages.
Support for "email gateway", where messages can be read and replied to using standard emails (like a mailing list).