Slack has several ways to send announcements, whether in a specific channel or for everyone in your entire workspace. Just type in the appropriate @mention with your message, then send.

Tip: To notify a specific group of members all at once, consider creating a User Group 💬  — available on the Standard plan and above. 

@here

The @here mention lets you notify just the members in a channel who are currently active in Slack.

@here is best for sending announcements that are relevant to members who are currently working or available.

@channel & @everyone

The @channel and @everyone mentions can be used to trigger desktop and mobile notifications for several members at once.

• @channel will send a notification to all members in the channel where you post the message. 
• @everyone notifies every member of your workspace. This command can only be used in the team-wide channel (usually called #general).
• Notifications will be sent to all members in the channel whether they are active or away.

When you use one of these @mentions, Slack will confirm the number of people you’ll notify and how many time zones are affected before sending the message.

Use care: This warning will only appear for workspaces with more than five members. Workspaces may also choose to turn this warning off entirely.

Settings and permissions

Workspace Owners can change who is allowed to use @channel and @here, plus turn warning messages for @mentions on or off, at my.slack.com/admin/settings. Under the Permissions tab, click expand next to Messaging for available options.

Note: If the use of @everyone is restricted to Workspace Owners and Admins only, then @channel and @here mentions in the #general channel can only be used by Workspace Owners and Admins as well.

Bot messages

If you wish to trigger one of these notifications with a bot message, the message should contain <!channel> or <!everyone>.