I have the Email Deliverability add-on and I haven't used it much but I do want to monitor what percentage of my emails are making it to the Inbox. While going through the settings, in the analytics area I noticed that they ask for a custom domain to be created. My IT department is hesitant to do this. Can someone please explain why it is needed and how it is used? We just don't want to do anything that might affect our reputation since we just migrated over to a dedicated IP.