• by George Bilbrey , Op-Ed Contributor, August 3, 2011

The email world can be tricky sometimes. There are a lot of terms that might sound similar (bounced and blocked), but aren't. And many ESPs use different terms for what may or may not be the same measurement (accepted and delivered). It can be very confusing to evaluate your email campaigns when you feel as if you are comparing apples and oranges.

The EEC has been championing the effort to standardize email terms and metrics (The SAME Project), but the adoption rates of these terms at the major ESPs has been slow.

So I'd like to offer an email glossary with some of the terms we see being confused most often. You can use this list to make sure that your reports and metrics mean what you think they are saying and that your campaigns are performing as well as you expect.

1.     Block: A refusal by an ISP or mail server not to accept an email message for delivery.  Many ISPs block email from IP addresses or domains that have been reported to send spam or viruses or have content that violates email policy or spam filters.

2.     Bounce:  A message that doesn't get delivered is said to have bounced. Emails can bounce for many reasons: the email address is incorrect or the account has been closed; the recipient's mailbox is full, the mail server is down, or the receiving system detects spam or offensive content.  (See "Soft Bounce" and "Hard Bounce")  For senders, hard bounces are the most important to pay attention to.  Specifically, the Unknown User is the most important hard bounce metric to look at, since it determines the quality of addresses on your file.

3.     Complaint Rate: The rate at which consumers are reporting mail as spam compared to the total volume of messages accepted and delivered.  People incorrectly assume that the complaint rate is based on the total volume of mail sent.  It is actually based on the total number of messages delivered to the inbox.  Therefore senders absolutely need to understand what their inbox placement rate is in order to accurately calculate their complaint rate.

4.     Delivered: Many marketers believe "delivered" means "delivered to the inbox," which isn't true at all.  Delivered means what is accepted at the webmail provider or ISP and includes email delivered to the inbox as well as to the spam folder. This is also known as accepted.  Senders should really be focused on what their inbox placement rate is.  That is the total number of messages delivered to the inbox minus spam folder deliveries, as well as bounced mail.

5.     Hard Bounce:  Email sent to an address where the message cannot be delivered due to a permanent failure.  This can be due to email users abandoning their account, or mailing to an address that has never existed.  In both cases, this type of hard bounce is called an Unknown User.  Hard bounces should not be retried because the error is considered permanent.   There are some exceptions that will require you to look closely at hard bounces.  For example, some ISPs may still return a hard bounce for a permanent block.  Looking at your hard bounce logs can determine if that's the case.

6.     Inbox Placement Rate (IPR): This is the number of emails actually being delivered to the inbox. Many factors impact your IPR, including complaint rate, spam trap hit rate and unknown user rate.  This term is commonly confused with delivered and accepted. Our research shows that the average IPR for IPs with Sender Scores of 91 or greater is about 88%, which is significantly lower than the 99% "accepted" rate that many ESPs report.

7.     Missing: Percentage of emails not delivered to any folder that the consumer has access to, including junk or bulk.  This could happen for a few reasons: the campaign isn't finished sending; nothing was sent to a seed list (where the data is pulled from); the ISP doesn't have a bulk folder; or the email was delivered to a folder that isn't being monitored. It could also be a message that had a soft bounce at the ISP, but because of retry methods, may eventually show up as Accepted/Delivered later.

8.     Open Rate: The number of HTML message recipients who opened your email, usually as a percentage of the total number of emails sent. The open rate is considered a key metric for judging an email campaign's success, but it has several problems. The rate indicates only the number of emails opened from the total amount sent, not just those that were actually delivered. Opens also can't be calculated on text emails. Also, some email clients allow users to scan message content without actually opening the message, which is falsely calculated as an open.  Open rate is often misclassified as meaning the render rate (render rate meaning messages where images were rendered).  People may still open and read emails in preview panes or with images off.

9.     Rejected: These are messages blocked during the SMTP session, due to policy, blacklisting or content.

10.  Soft Bounce:  Email sent to an active (live) email address that is turned away before being delivered. Often, the problem is temporary -- the server is down or the recipient's mailbox is over quota. The email might be held at the recipient's server and delivered later, or the sender's email program may attempt to deliver it again. Soft-bounce reports are not always accurate because they don't report all soft bounces or the actual reason for the bounce. 

What other terms do you often see confused or muddled?