I recently posted a question inviting people into a discussion on a rather big mailing list. I got a few responses, but stopped getting those a few hours later. At the same time, other topics continued to develop. I had this thought that perhaps if the mailing list was divided into smaller categories, perhaps I would get more responses. Is this assumption true? What factors does it depend on?
The way you create smaller categories on an email list is to create other email lists, since the technology for email lists is pretty basic (send message, distribute to all subscribers). You might have more options on a web-based community; I'm focusing on email in this answer.
Your goal is to reach the greatest number of people who are interested in your topic before other messages push yours off the bottom (so to speak). The advantage of a large list is that the people are there; the disadvantage, as you've noted, is that there are lots of messages so yours is less visible. It's sort of like the difference between Stack Overflow and Community Building. :-)
If you create sub-lists for certain topics:
- Some people won't bother to subscribe.
- Those who do subscribe are more interested, on average, than the people on the main list.
- It's easier to filter incoming email into folders.
- The list may go through periods of dormancy between bursts of activity, depending on how "niche" your topic is.
If you use one big list:
- Everybody's there, including the people who are kind of interested in your topic but not enough to subscribe to a list about it.
- Everyone's there, so there will be a lot of content that is not about your topic.
- People are already there and inertia is a powerful force.
- If you can instill the culture, you can encode certain topics in the subject line.
- People interested only in certain topics are more likely to drop out because of the other content. (Filtering mitigates but does not eliminate this factor.)
As a case study, I'm going to talk about a family of mailing lists that I've participated on for many years (so I've been able to observe trends). These are the mailing lists for the SCA, a large historical-study organization.
In the beginning there was "the SCA mailing list". It was called the Rialto because it was the place everybody came for news. When there were only a few hundred people on the mailing list this worked, but as more and more people joined, each person saw more messages that he considered to be noise. Two kinds of fragmentation happened: by topic and by locale.
The SCA is divided up into regional groups (kingdoms). Each kingdom has its own mailing list (or perhaps more than one). Each kingdom has its own bureaucracy and official newsletter and borders, so "stuff about the kingdom" is usually pretty identifiable as such to the person deciding where to post. The lists (that I've seen) tend to be a mix of announcements from kingdom officials and discussion of said announcements, kingdom policies, followup from recent gatherings, and general chit-chat.
The SCA also covers a wide range of topics of interest, ranging from embroidery to music to archery to dance to fencing (and many more). Early on, as sub-communities felt drowned out on the Rialto they spun off mailing lists for specific topics. More recently, sometimes topic-specific lists have spun off from kingdom lists, resulting in (e.g.) a brewers' list and a brewers' list for a kingdom where there's a concentration of brewers. Somebody living in that kingdom who's interested in brewing will probably subscribe to both lists; somebody from another kingdom will probably only use one of them (and might not even know about the other).
Now, the fact that these topic-specific lists exist doesn't mean those conversations don't also happen on the general lists. A discussion on a kingdom list might start out talking about the dancing at a recent gathering, which leads somebody to ask about one of the dances that was taught, which leads to a discussion of dance research, and maybe the music gets brought in along the way too. Meanwhile, those guys over on the dance email list who aren't on the kingdom list have no idea about that unless somebody cross-posts.
Does it sound like I'm describing the problem of fragmentation? Why yes I am. It's the other end of the spectrum from "one big list", and it's something you need to be aware of.
Now, all that said, many people wouldn't bother to read "one big list" today; in fact, I believe the Rialto survives only in the form of a Usenet group, if anybody still pays attention to Usenet. Casual community members follow one or two lists; people who are avid about a particular topic will seek out the others; and in general, nobody's getting everything that he's interested in but most people find a balance.
Conclusion: if your email community is large and active enough that some people are dropping out because of volume and others are feeling drowned out, and there is a large-enough contingent of people interested in a subtopic to sustain another community, then it's worth creating an additional list. Assume that interested people will stay subscribed to the original, that conversations might now happen on either list, that some people won't follow you to the new list -- but those who do will have the chance to have more in-depth conversations about their topic of interest than they would have on the original list.