For your sales reps, the activity timeline rules the screen. Now the timeline shows an activity when a list email has been sent to a lead or contact. This change applies to Lightning Experience only.
List email activities only appear in the activity timeline if logging list email activities is on. It is turned on by default.
Your reps can’t create a list email in the Salesforce for Android, Salesforce for iOS, or Salesforce mobile web, but you can still see the activity.