The MNO combination is powerful but complex and buggy. This outlines an approach to understanding what is going on.
Messaging http://drupal.org/project/messaging & Notifications http://drupal.org/project/notifications (M & N) are two modules maintained by the same team and released together. Organic Groups http://drupal.org/project/og (OG) is maintained by another team.
Together these can be very powerful. My use case is replacing an email messaging system in majordomo. The MNO combination allows me to create multiple overlapping lists very easily, each with its own degree of privacy. It is also more sensible to upload large files to the server and allow others to download as needed, rather than sending through email (and majordomo chokes on large files). The combination also gives the best of an online forum, with email notification when something needs to be looked at.
The notifications part of OG is explicitly related to M & N but releases do not coincide with M & N. It is not always clear which versions of OG, whether stable or development, go with which versions of M & N, which can also be stable or development.
The interaction of multiple message templates, message methods, digest types and intervals is very complex and, as far as I can tell, undocumented. You need to understand it before you launch a live site. I don't claim to be a Drupal expert at all, but the only disaster I have had so far on a live site is performing a minor upgrade to one of these modules ....
These tips really apply to a test site therefore.
1) I have only tried simple mail. To make it work, you need to add the line break converter before the HTML to text filter in the Messaging Plain Text input format.
2) If you are using FCK editor, exclude the paths admin/messaging/template/* otherwise the templates fill up with unwanted paragraph tags etc. Presumably similar considerations apply to other wysiwyg editors.
3) It is easiest to see the templates if you use phpMyAdmin or a similar tool on the table messaging-message_parts, but the table is only populated for templates that have previously been saved. You don't need to edit any of the fields within each template, just open the template section and press [Save] for each template.
4) It is useful to add a code to each template so you can see where bits of email have come from, eg [NENC] for notifications-event-node-comment. You need to add this for each field in the template (subject, ehader, body etc). Note that the db table does not use the same vocabulary as the UI - the db uses insert node and the UI uses create node. I have used acronyms from the db table.
5) Create notification intervals called short and long, with times of 1 minute and 2 minutes and digests of short and long respectively. The inbuilt immediate interval and these two intervals allow testing of digest combinations. You cannot have more than one interval of the same length and the UI will not let you process the "1 hour" interval more than hourly. My test site does not have an automatic cron run, so I can set up some tests then process them all at once to see what happens to the emails.
6) Create dummy users. I think you should have 5, plus the superuser.
Dummy1, Dummy2 and Dummy3 get intervals of immediate, short and long respectively. (see above)
Dummy4, Dummy5 and Superuser are used to create posts and comments.
In this scenario, D1-3 are "receive only" and D4-5 & SU are "send only". At a later stage you might want to see what happens when some users both send and receive (which is of course the usual behaviour)
7) Use Admin_Menu and Devel tools. Enable switch-user for all the dummies. Use the "Group details" block. These steps will enable you to create posts and comments for several users then quickly switch to the queue admin tool.
I intend this to be a strategy document (and I hope others will contribute) and I won't highlight errors here that are version dependent. Areas to be studied however include
A) The subscription interface
- whether subscriptions are to groups or content within groups - they behave differently.
- the bulk subscription interface - works (partially) with some combinations of module versions and not others.
- whether users can edit their own subs, and what the superuser can edit. Access can get refused at odd times, even for the superuser.
B) Which templates are used. The OG templates seem only to be used for subs to topics, not the groups themselves. Once you understand this, or at least the parts your site seems to use, you can alter the templates to suit!
C) Whether the site default methods for interval etc are implemented - in some circumstances individual users or subs get a value of never by mistake.