One practice that seems relatively common is for an organisation to have two main mailing lists, one for serious discussions that are expected to be relatively topical and another for anything that’s not overly offensive. Humans are inherently incapable of avoiding social chatter when doing serious work. The people who don’t want certain social interactions with their colleagues can find it annoying to have both social and serious discussions on the same list. While the people who want social discussions get annoyed when people ask them to keep discussions on topic.
Organisations that I have been involved with have had mailing lists such as foo-chat and foo-talk for social discussions that involve the same people as the main list named “foo“, as well as having list names such as “memo-list” for random discussions that are separate from a large collection of lists which demand on-topic messages.
The Debian project has some similar issues with the debian-private mailing list which is virtually required reading for Debian Developers. One complication that Debian has is that the debian-private list has certain privacy requirements (messages will be declassified after 3 years unless the author requests that they remain secret forever) which make it more difficult to migrate a discussion. You can’t just migrate a discussion from a private list to a public list without leaking some information. So it seems to me that the best solution might be to have a list named debian-private-chat which has the same secrecy requirements but which is not required reading. As debates about what discussions are suitable for debian-private have been going on for more than 3 years I don’t think there’s any reason not to publish the fact that such discussions take place.
Also it seems that every organisation of moderate scale that has a similar use of email and for which members socialise with each other could benefit from a similar mailing list structure. Note that I use a broad definition of the word “socialise” – there’s a lot of people who will never meet in person and a lot of the discussions are vaguely related to the main topic.
I wonder whether it might be considered to be a best practice to automatically create a chat list at the same time as creating a serious discussion list.