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

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

@here

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

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

@channel & @everyone

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

• @channel will send a notification to all team members in the channel where you post the message. 
• @everyone notifies every member of your team. This command can only be used in the team-wide channel (usually called #general).
• Notifications will be sent to all team 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 teams with more than 5 team members. Teams may also choose to turn this warning off entirely.

Settings and permissions

Team Owners can change channel notification settings and permissions, 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 Team Owners and Admins only, then @channel and @here mentions in your team's #general channel can also only be used by Owners and Admins.

Bot messages

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