Tribe does not offer an option to run email campaigns. However, if you are using Tribe's SendGrid app, in Sendgrid, you are able to get the list of the email from all the members in a specific group(s), and then send a mass email to all. This is a way to contact your members somewhere outside of the community.
Now, if you want to make sure that members in a specific group can see an announcement, you can:
1. Post your announcement as a post in the group, then pin the post to the top of the group page. All your group members can see that post anytime they visit the group. How to pin a post to the top of a group? 8
2. If you want to notify your group members about the announcement, before you post if in the group, you need to make sure that the email notification for the group is enabled. This way, when you post the announcement in the group, all the group members will receive an email notification. How to enable group notification?12
If you don't want group members to receive email notification for all the post in the group, you can turn off this option after a few minutes.
If you don't have SendGrid, I hope this workaround can help.