What Is Email Delivery?
Email delivery is the measure of how many of your emails were accepted by an inbox provider.
Often confused with email deliverability, delivery is not the act of making it into the inbox (and avoiding the spam folder).
When your email is delivered that means the ISP (inbox service provider, like Gmail or Yahoo) has accepted your email. Your email has yet to be sorted into a folder like Inbox, Spam, or Promotions.