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Email Lifecycle and Event Types

When you use SendPost API to send an email, the message goes through a complete lifecycle with various events. Understanding each event type and its significance will help you track your email delivery and engagement effectively.

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Initial Processing Stage

1. Processed (Type 0)
  • What it means: This is an acknowledgement that SendPost has successfully processed your email request and forwarded it to the SMTP machine for delivery.
  • When it occurs: Immediately after SendPost accepts your API request and validates the email.
  • Significance: This confirms that your email was accepted by SendPost and is queued for sending. It does not mean the email has been sent yet.
2. Dropped (Type 1)
  • What it means: The email was dropped before delivery attempts were made.
  • When it occurs: If the email address is invalid, malformed, or exists in your suppression list.
  • Significance: No delivery attempt will be made. The email will not be sent to the recipient.

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Delivery Stage

After the email is processed, SendPost forwards it to the SMTP machine. When the SMTP machine actually sends the email, it will result in one of the following outcomes: 3. Delivered (Type 2)
  • What it means: The email was successfully delivered to the recipient’s mail server.
  • When it occurs: After the SMTP machine sends the email and receives a successful delivery confirmation from the recipient’s mail server.
  • Significance: The email reached the recipient’s mail server. Note: This does not guarantee the email reached the inbox (it could be in spam) or that the recipient has read it.
4. SoftBounced (Type 3)
  • What it means: The recipient’s mail server temporarily rejected the email (e.g., mailbox full, server temporarily unavailable).
  • When it occurs: When the recipient’s mail server returns a temporary error code.
  • Significance: SendPost will automatically retry delivery for soft bounces. There can be a delay between when the email is sent and when the final outcome (Delivered, HardBounced, or remains SoftBounced) is determined due to these retry attempts.
5. HardBounced (Type 4)
  • What it means: The recipient’s mail server permanently rejected the email (e.g., invalid email address, domain doesn’t exist).
  • When it occurs: When the recipient’s mail server returns a permanent error code.
  • Significance: No further delivery attempts will be made. The email address gets added to your suppression list.
Important: After the SMTP machine sends an email, you will receive exactly one of these four events: Delivered, SoftBounced, HardBounced, or Dropped. For soft bounces, there may be a delay between when the email is sent and when the final event is generated due to automatic retry attempts.

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Post-Delivery Engagement Stage

Once an email has been delivered, recipients may interact with it, generating additional events: 6. Opened (Type 5)
  • What it means: The recipient opened the email (requires open tracking to be enabled).
  • When it occurs: When the recipient opens the email and the tracking pixel is loaded.
  • Significance: Indicates engagement. Note: Some email clients block images by default, which may prevent open tracking.
7. Clicked (Type 6)
  • What it means: The recipient clicked a link in the email (requires click tracking to be enabled).
  • When it occurs: When the recipient clicks a tracked link in the email.
  • Significance: Indicates strong engagement and interest in your content.
8. Unsubscribed (Type 7)
  • What it means: The recipient clicked the unsubscribe link in your email.
  • When it occurs: When the recipient uses the unsubscribe link (typically the {{unsubscribe}} template variable).
  • Significance: The recipient will be automatically added to your suppression list and will not receive future emails.
9. Spam (Type 8)
  • What it means: The recipient marked your email as spam.
  • When it occurs: When the recipient reports your email as spam through their email client.
  • Significance: This negatively impacts your sender reputation. The recipient will be added to your suppression list.

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Key Concepts

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Processed vs Sent

  • Processed (Type 0): An acknowledgement that SendPost has processed your email request and forwarded it to the SMTP machine. This does not mean the email has been sent yet.
  • Sent: When the SMTP machine actually sends the email out. This happens after Processed, and you won’t receive a separate “Sent” event. Instead, you’ll receive one of the delivery outcome events (Delivered, SoftBounced, HardBounced, or Dropped).

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Delivery Outcomes

After the SMTP machine sends an email, exactly one of these four events will be generated:
  1. Delivered: Successfully delivered to the recipient’s mail server
  2. SoftBounced: Temporarily rejected (with automatic retries)
  3. HardBounced: Permanently rejected (no further attempts)
  4. Dropped: Dropped before delivery attempts (invalid address or in suppression list)

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Multiple Events Per Email

For a single email message, multiple events can be generated throughout its lifecycle:
  • You’ll always receive a Processed event
  • You’ll receive exactly one delivery outcome event (Delivered, SoftBounced, HardBounced, or Dropped)
  • You may receive multiple engagement events (Opened, Clicked, Unsubscribed, Spam) if the recipient interacts with the email
The emailMessage object in webhook payloads remains the same across all events, allowing you to correlate events using the messageID.
For detailed information about the webhook payload structure, including SMTP codes and custom headers, see SendPost Webhook Object.