| SMTP response code | |
| 0 | No emails have been sent to the subscriber yet. |
| 200 | Delivery successful. |
| 4xx or 5xx | SMTP status codes. |
| 1001 | Subscriber unsubscribed in the latest campaign. |
| 1002 | Subscriber reported the latest campaign as spam. Is automatically unsubscribed. |
Look at more examples from The most common response codes.
| Classification | |
| ok | Message has been successfully delivered. |
| bad-mailbox | Message recipient is non-existent, inactive or disabled. |
| blocked | Delivery has been denied from Smaily (or any service). |
| expired | Message delivery has taken more than the maximum amount (2 days) of time. |
| inbox-full | Mailbox quota overused by recipient. |
| message-size | The message is too large for the receiving email server. |
| routing-error | Invalid (or non-existent) DNS entry or domain name. |
| signature-error | Incorrectly configured SPF or invalid DKIM signature. |
| spam | Message has been identified by the receiving email server as SPAM. Determined by the content or sender of the message. |
| transit-error | Hourly/daily sending limits exceeded, receiving system is under heavy load or undergoing maintenance. |
| unknown | Message status unknown. |