To limit who can send email to your channel, go to the channel name, click More options > Get email address, then click the advanced settings link.
From there, you can manage who is able to access the email address for that channel. You can restrict the audience to include only members of the team that owns that channel, or narrow your audience to specific domains. You can also remove your current email address entirely.
Note: If your IT admin has disabled the ability to send email to channels, the Get email address option won't appear.
Head to the desktop or web app to manage who can send email to a channel.