I want to have a special channel primarily to post company’s announcement in my Slack team, and I don’t want anybody, except me and a select few people, to post in that channel, to not distract the channel viewer from the announcement content. But I still want everybody to be able to see the content of the channel (e.g. making it one of the default channels new user automatically joins to). Can I do that in Slack? How? Or is there an alternative or workaround to achieve the similar result?
You can restrict who can post to the #general channel on your team settings, in http://my.slack.com/admin/settings#permissions
Available restrictive options are Team Owners and Admins or Team Owners only.
You can rename #general to something more appropriate like “#announcements”.
Currently, you cannot restrict posting rights to other public channels than #general.
More information is available on https://get.slack.help/hc/en-us/articles/220105027-The-general-channel