Add a note on direct messages

Author: arunkannawadi

communications/slack-culture.rst

@@ -83,6 +83,19 @@ You can save space, time, and distractions to others by using commonly understoo
 
 -  ``:thank_you:`` (🙏) or ``:thankyou:``
 
+.. _slack-direct-messages:
+
+Direct messages
+---------------
+
+Please keep direct messaging to a user or a set of users to minimum.
+Direct messages should be avoided for any technical discussions or asking for support, even if you are sure that you have involved all those who are interested or who can contribute.
+Instead, such discussions should be in a thread in an appropriate :ref:`discussion channel<slack-discussion-channels>`.
+Direct messages shoul be reserved for conversations on topics such as code review requests, logistics, or on other topics not directly related to work.
+See this `community post`_ for why direct messages are considered harmful.
+
+.. _community post: https://community.lsst.org/t/dms-in-slack-considered-harmful/4036
+
 .. _slack-snippets:
 
 Text snippets and posts
@@ -191,7 +204,7 @@ If you need to have a group created because you have a routine need to @-mention
 @-mentioning a particular user notifies that user and adds the message to their "Mentions & reactions" list.
 Be aware of the person's timezone before @-mentioning them.
 If you need to @-mention them outside normal hours, you may want to schedule the message to be posted later (using the ``/send`` or more sophisticated ``/schedule`` shortcuts from `Timy`_).
-Sometimes @-mentioning a user can be helpful to disambiguate replies in a multi-person conversation, but if you find yourself prefixing every message you send with an @-mention, consider whether it is implied by context or whether the whole conversation might be better in a thread or in direct messages to that user.
+Sometimes @-mentioning a user can be helpful to disambiguate replies in a multi-person conversation, but if you find yourself prefixing every message you send with an @-mention, consider whether it is implied by context or whether the whole conversation might be better in a thread.
 
 .. _Timy: https://timy.website/#commands