Email is still one of the most widely used Internet tools and, as such, a great marketing tool not to overlook. Like other web marketing tools, email marketing has an advantage in that it is also highly measurable. That said, there remains much confusion among professionals on how to measure email marketing and what metrics are reliable. Recently the industry group the Email Experience Council finally defined standards for email marketing measurement, as the Web Analytics Association did in 2007 for websites.
The historical email marketing metrics
Before considering the new metrics definitions, its worth understanding what metrics have historically been used in order to better understand the rationale underlying the EEC standards.
|The number of messages we sent from our server.||An accurate metric|
|The number of messages don't bounce back, i.e. aren't returned as undeliverable.||Unreliable: we generally do not know how many messages were discarded by an ISP ("dropped on the floor") as spam or placed in a recipient's spam folder.|
|The number of messages displayed to a user.||Counting open messages requires that a tiny image is downloaded from a central server. For several years, most email clients (Outlook, Apple Mail, Thunderbird) and webmail block images, especially those from unfamiliar senders. Plain text messages were never measurable. Highly unreliable.|
|The number of messages in which a user has clicked a link (interacted).||Highly reliable IF tracking code was placed on the link.|
|The number of messages displayed to a user or the number of messages where the user clicked on a link.|
|The number of goals reached, thanks to the email campaign.||Highly reliable IF tracking code was added to link and web pages.|
The standard email marketing metrics defined by the Email Experience Council
Definitions relating to delivery metrics
Any email that is not rejected by a server, including emails delivered to the inbox, spam or junk folders or those are missing from those folders that did not receive a bounce reply.
sent - bounced = accepted
The total amount successfully delivered to the server divided by the total e-mail deployed (unique records). The amount successfully delivered is the total amount attempted minus all failures, including hard bounces.
accepted emails / sent emails = accepted rate
A message rejected by the receiving server. Typically bounces are referred to as either hard bounce, a delivery failure for permanent reason (e.g. a misspelled email address) or soft bounce, a delivery failure due to a temporary condition (e.g. mailbox is currently full).
hard bounce + soft bounce = total bounces
Inbox Placement Rate
The ratio of emails that are delivered specifically to the recipient’s inbox divided by the total emails sent.
delivered to the "inbox" / total sent = "inbox" placement rate
Definitions relating to Open metrics
Confirmed Open Rate
Is the percentage of unique confirmed opens divided by the total number of accepted emails. While unique is the preferred method, this rate may be calculated using either the unique or the total confirmed opens.
Editor's note: Plain text messages are only counted when a user clicks on a link in the message.
This metric can be calculated as total (t) or unique (u).
confirmed opens (t/u) / accepted = confirmed open rate (t/u)
Email Render Rate
The number of times an email is displayed (whether fully opened or within the preview pane) and recorded using a tracking image within an HTML format message and divided by the total and expressed as a percentage. While unique is the preferred method, this rate may be calculated using either the unique or the total email renders.
email renders (t/u) / accepted emails = render rate
Average Recipient Render Rate
The total number of times an email is rendered (whether fully opened or within the preview pane) and captured using a tracking image within an HTML format message divided by the unique number of emails rendered, expressed as a percentage.
total renders / unique renders = average recipient render rate
Aimed as secondary metric, it provides insight into the average number of times each recipient (that renders a message at least once) views an individual message. This may be of value to senders with deep content and/or content that has a long shelf life, (e.g. newsletters) assuming that a high number of renders per recipient is a positive for certain types of email programs. This metric may also be calculated using Confirmed Opens if that is more applicable for the sender.
Definitions related to click metrics (engagement)
Click Through Rate (CTR)
The number of times a link is clicked from a message divided by the number of accepted messages. For example if a message is sent to 4 people and two people open the message, downloading the images. One of two that opened the email clicked on a link one or more times, the resulting CTR for that link is 25% (1 unique clicker/4 accepted emails = 25%).
clicks (t/u) / accepted emails = click through rate (t/u)
This metric may be calculated as Unique CTR, which refers to the number of people that clicked or total CTR, which refers to number of clicks for a specific link.
Email marketers also often calculate CTR for the entire email to compare several emails within a campaign or across campaigns.
Click to Open (CTO)
The unique number of times a link is clicked from a message divided by the unique number of confirmed opens for that message. For example if a message is sent to 4 people. Two people render the email, and one of those two click on a link one or more times, the resulting CTO is 50% (1 click /2 confirmed opens = 50%).
clicks / email renders = click to open rate (t/u)
Again, this metric may be calculated as Unique CTO, which refers to the number of people that clicked or total CTO that refers to number of clicks for a specific link.
The Click to Open rate may also be calculated for the entire email rather than an individual link.
A cautious note on the limitations of the new open definitions
There is in fact no reliable way to determine how many recipients have truly displayed an email. Accordingly, the confirmed rate of openings will be much lower than what has occured in fact – the metric is a low estimate. The render rate suffers even more from this problem.
From the official definitions one notes that the metric "conversion" was not included. Conversion is still an essential measure for the calculation of how effective an email campaign has been.
Email marketing metrics: summary table
|Delivery metrics definitions|
|sent – bounced = accepted||Yes|
|accepted emails / sent emails = accepted rate||Yes|
|hard bounce + soft bounce = total bounces||Yes|
|delivered to the inbox / total sent = inbox placement rate||No|
|Open metrics definitions|
|confirmed opens (t/u) / accepted = confirmed open rate (t/u)||No|
|email renders (t/u) / accepted emails = render rate||No|
|Average Recipient Render Rate||total renders / unique renders = average recipient render rate||No|
|Engagement definitions (link clicks)|
|clicks (t/u) / accepted emails = click through rate (t/u)||Yes|
|clicks / email renders = click to open rate (t/u)||No|
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