How well do the biggest email senders do at reaching the inbox?

UPDATE (10/24): In our original post, we used the term “delivery rate” instead of the more commonly used term “message accepted rate”. The analysis below is accurate; however, we will follow up soon with a more comprehensive analysis that reveals the proportion of messages that are accepted/bounced after initial phases of rejection such as IP rate limiting and recipient checks. This will give us better insight into which messages were rejected due to content issues.

We analyzed millions of inbound email delivery attempts by looking up the abuse contact information for each connecting IP address in the fantastic Abusix abuse contact database . The following table shows you what percentage of the email from these sending networks and providers actually gets delivered to the inbox of recipients.

We need to take our hats off to MailChimp for their 99% delivery success rate. We know MailChimp takes pride in their aggressive approach to policing spam and bad delivery practices in their enormous user base. These numbers back up the value of that technology investment.

Surprisingly, Google and Microsoft are achieving only a mid-80s delivery rate from their services. This implies that a good proportion of the email from their users is unwanted — in other words, spam.