If using Subsplash Messaging, the Group sync feature of the Rock Plugin allows a bidirectional sync of Group membership for your People. For more information on Subsplash Groups & Messaging, see this article.

After initial setup of the plugin, make sure to check the Group Sync Enabled box within the Settings of the plugin.

Installed with the plugin is a group attribute value that you will need to make available on any Group Types you wish to sync with a Subsplash group.

You can do so under Admin Tools > General Settings > Groups Types

Once it's available in the Group Type, navigate to a group and set the Subsplash Group from its dropdown now under Group Attribute Values

Lastly, create a job to sync group members as often as you need. With the plugin a Job Type will be installed called "Sync Subsplash Groups (Plugin)" and you will want to create a Job with it set to your ideal sync timeline.