Understanding Delivery Metrics in Letterhead

In Letterhead, understanding email delivery metrics is crucial for assessing the success of your email campaigns and maintaining a healthy sender reputation.

Once a newsletter is published, Letterhead displays the delivery metrics as a report within the application.  To view these metrics, go to Newsletters, and click on any of your published editions, and the Report will load, instead of the composer screen.

Understanding Engagement Metrics

Emails sent 

This is the number of audience members that were targeted; in other words, number of audience members that Letterhead tried to send your edition to.  Usually, this is the full list of your subscribers at the time of your send; however, some may be suppressed immediately.

Suppressed or admin bounces means that the email servers have indicated that these addresses either do not exist or have been inactive for an extended period. These addresses are not targeted in your email sends.  In other words, these audience members were excluded automatically and did not hurt your reputation.

Open rate

This is the percentage of unique recipients confirmed to have opened your newsletter, and it is based on Unique confirmed opens divided by the Accepted metric.

Open rate = Unique confirmed opens / accepted.

Legacy open rate

Percentage of top pixels rendered from emails sent.  This is the traditional open rate provided by newsletter services, but it is not an accurate metric of confirmed subscribers or readers engaging with your newsletter content because it does not exclude bots or opens by apps to check for spam.

Clickthrough rate

Percentage of emails that had at least one link clicked in the email, and it is based on Unique clicks divided by the Accepted amount.

Clickthrough rate = unique clicks / accepted.

Initial renders

Number of times emails were displayed, as recorded by top open pixels.

Unique confirmed opens

Number of emails displayed, or that had at least 1 link clicked.  This may have a 5% error threshold.

Total clicks

Number of link clicks in total, across all emails sent.  More than one click on one same email will count.  So, if one email, had several links clicked, each click would count.

Unique clicks

Number of emails that had a link clicked, but more than one click on one same email will not be counted.


Number of audience members that unsubscribed via Letterhead's unsubscribe link in the footer of your template.

Delivery metrics


This metric, in our system, assumes that the emails have been successfully delivered to a mailbox.


The accepted metric is calculated as (sent - soft bounces), and all of your engagement metrics are based off the Accepted number. It represents the number of emails successfully delivered to recipients' mailboxes after excluding soft bounces.  


The number of bounced emails encompasses hard bounces, soft bounces, and block bounces. This metric reflects the total number of bounces encountered in your email campaigns.  Letterhead does not display a specific bounce rate for individual newsletters in published newsletter metrics. Instead, it considers various bounce types collectively.

Types of Bounces:

  • Soft Bounces: Soft bounces are temporary delivery issues. For example, a soft bounce may occur if a recipient's inbox is temporarily full. Letterhead will continue attempting to deliver emails to soft bounce addresses for a limited time, as the issue may be resolved.

  • Hard Bounces: A hard bounce refers to a permanent delivery issue. These are typically caused by factors such as invalid email addresses or domains. When an email address consistently returns a hard bounce, Letterhead categorizes it as a bounced address. Future emails will not be sent to such addresses to maintain your sender reputation. With hard bounces, Letterhead is going to, over time, automatically update these audience members to have a "bounced" status, which will decrease the size of your total subscribers.
  • Block Bounces: Block bounces result from a permanent IP block. These occur when a recipient's email server decides to block emails from your IP address due to various reasons, such as a history of spam complaints.

Note: soft bounces, block bounces, and undetermined are usually temporary events, unlike hard or admin bounce-type events, which are permanent.

For more information on how Letterhead handles email bounces, please refer to this article.