The metrics regarding email deliverability are slippery, seemingly impossible to pin down. Certainly, email service providers vary greatly in what they track and how they do it. Hard bounces, for example, may seem like the easiest to manage, but a shocking number of companies fail to properly clean their lists and some ESPs simply may not report all attempted delivery failures. In today’s world this presents a great threat to reputation and engagement, sending valid and even optedin emails to the spam folder.