Having insight into how your emails are processed and engaged with is key to having a healthy and successful email program. To help, SendGrid (Cetain's 3rd Party Email Provider) has robust analytics and tracking capabilities.

As emails are sent and recipients interact with them, events are triggered within SendGrid. SendGrid customers can be enabled with Event Webhooks to receive notifications for the nine types of email events described below. Some are informational and can be used to create instant dashboards. Others you may want to save to query later. And there are some events you may want to react to immediately.

Below is a quick breakdown of each of the nine events:

1. Processed (Tracked by Certain)

This event fires when SendGrid receives an individual message and prepares it to be delivered. Think of this as the top of the funnel-unless it is dropped (see below), each message you push to SendGrid will create a processed event.

2. Dropped (Not Tracked by Certain)

There are a number of reasons your email will not even be sent to a recipient for delivery. This event informs your system when an email has been dropped. Further, it provides a reason for the drop, such as if we’ve found spam content (if spam checker app is enabled) or we see the recipient has unsubscribed previously.

3. Deferred (Tracked by Certain)

When an email cannot immediately be delivered, but it hasn’t been completely rejected, the deferred event fires. Sometimes called a soft bounce, SendGrid will continue to try for 72 hours to deliver a deferred message. After 72 hours, the deferral turns into a block.

4. Bounce (Tracked by Certain)

If a server cannot or will not deliver a message, SendGrid fires a bounce event. Bounces often are caused by outdated or incorrectly entered email addresses. Many times you won’t know a bounced email address until it bounces, so this event can help you ensure it doesn’t bounce again by removing it from your lists.

5. Delivered (Tracked by Certain)

When an email has been accepted at the receiving server, the delivered event fires. This event does not guarantee that the email was placed in the recipient’s inbox. In fact, a delivered email is only the beginning of an opaque process. The remaining four events begin to give us hints about whether anyone will ever see this delivered email.

For more information on the first 5 events mentioned above, read the following post from our delivery expert, Will Boyd: Delivered, Bounced, Blocked, and Deferred Emails: What Does It All Mean? 

6. Open (Tracked by Certain)

An opened email is the first step toward the action you want your recipient to take. This event fires every time your email is viewed with images turned on. Like all email service providers, SendGrid uses a transparent image beacon to track opened messages. This beacon is currently the only way a sender can tell if an email has been opened.

(To learn how image opens are affected by Google’s new image caching, read our blog post on the topic here.)

7. Click

The click is the pinnacle of email engagement! Your call to action, whether it is to confirm a newly registered account or to view a recommended product, asks the recipient to click a link. SendGrid tracks that interaction and fires a click event.

8. Spam Report (Not Tracked by Certain)

Most Internet Service Providers (ISPs) provide a feedback loop, sending specific spam complaints to the Email Service Providers (ESPs), like SendGrid. When SendGrid receives a notice, we fire a spam event, so that you can react appropriately—or at the very least, never send another email to that address!

9. Unsubscribe (Not Tracked by Certain)

One of the most important events fires when a recipient unsubscribes from your mailings. Reacting immediately to an unsubscribe by removing the email from your lists can pay long term dividends in fewer spam reports and a higher engagement rate.

Source: https://sendgrid.com/blog/the-nine-events-of-email/