This article explains how to check in Email Live Tracking why an email was not delivered.
If an email does not reach the recipient, you can check the delivery status in the Control Panel. The Delayed and Rejected delivery statuses are particularly important.
Checking the delivery status in Email Live Tracking
- Sign in to the Control Panel using your administrative credentials.
- Go to Email Security > Email Live Tracking.
- Search for the affected email.
- Filter or sort by the Delayed or Rejected delivery status.
Understanding delivery statuses
| Delivery status | Meaning |
|---|---|
| Delayed | The email could not be delivered yet. Hornetsecurity continues trying to deliver the email. |
| Rejected | The email could not be delivered or was rejected by the destination server. |
These statuses are also represented by symbols in Email Live Tracking:
| Symbol | Meaning |
|---|---|
| Clock | The email is delayed. Additional delivery attempts will be made. |
| X | The email cannot be delivered or was rejected by the destination server. |
Viewing SMTP error details
To check the reason for the failed delivery, open the SMTP information for the affected email.
- In Email Live Tracking, open the context menu for the affected email.
- Click Email Details.
- Open the SMTP tab.
- Check the displayed SMTP code and the response from the destination server.
The SMTP tab shows why the email could not be delivered. For incoming emails, this message generally comes from your destination server.
Example code:
2026-09-14T12:24:29Z;TLS;xx.mail.protection.outlook.com[X.X.X.X];451 4.4.4 Mail received as unauthenticated, incoming to a recipient domain configured in a hosted tenant which has no mail-enabled subscriptions. ATTR5 [DB5PEPF00014B9E.eurprd02.prod.outlook.com 2026-09-14T12:24:30.153Z 08DF10E627437FE1];RCPT_TO;CIPHER=STRONG;IDENTITY=CA_VERIFIED;TLS_VER=TLSv1.3;TLS_CSUITE=TLS_AES_256_GCM_SHA384;TLS_WARN=NONE
Interpreting the SMTP code
The SMTP code indicates why an email was not delivered.
Common causes include:
- Destination server is temporarily unreachable
- Mailbox does not exist
- Mailbox is full
- Destination server rejects the email
- Destination server does not currently accept connections
- Configuration of the destination system prevents delivery
For incoming emails, the cause is often with the destination system if the destination server rejects the email or is unreachable.
What should you do?
Depending on the displayed status and SMTP code, check the next steps.
| Situation | Next step |
|---|---|
| Email is Delayed | Check whether the destination server is reachable. Hornetsecurity will make additional delivery attempts. |
| Email is Rejected | Check the SMTP code and the response from the destination server. |
| Destination server rejects the email | Check the configuration of the destination server or contact the administrator of the destination system. |
| Mailbox does not exist | Check whether the mailbox was created correctly. |
| Error is unclear | Contact Hornetsecurity Support with the SMTP code, sender, recipient, and timestamp. |
Further information
You can find a list of Hornetsecurity SMTP codes in the manual.
For more information about automatic delivery when the mail server is temporarily unreachable, see the article “Automatic delivery of emails when the mail server is temporarily unreachable”.