This idea was submitted in 2013. It's nearly two years later and we still do not have the ability to log whether a sales email was delivered.
This is especially frustrating, as we would like alerts set up depending on whether a sales email was delivered in X timeframe after send. The only confirmation we have is if the email hard bounced (which can also take up to 36 hours) or rely on the fact the Email send is listed on the Lead's MSI as a confirmation it was delivered.