Kentico create new Custom Acitivity
ActivityInfo activity = new ActivityInfo();
activity.ActivityTitle = "Newsletter Email Bounce";
activity.ActivityValue = "some email address";
activity.ActivityContactID = ContactID;
activity.ActivitySiteID = SiteContext.CurrentSiteID;
activity.ActivityType = "NewsletterEmailBounce";
activity.ActivityContactGUID = ContactGUID;
activity.Insert();