When your server has failed to perform a requested transmission, it will let you know by sending your client a FAILED_TX message.
The format for a FAILED_TX message is:
FAILED_TX tag code [detail]
where
| tag | is the label of the message that didn't make it; |
| code | is the failure code in hexadecimal; and |
| detail | is an optional envelop detailing the error |
Failure codes are defined as follows:
| value | name | meaning (in the voice of the sender's server) | additional fields |
|---|---|---|---|
| 0xA801 | NAK_ZONE_UNKNOWN | I cannot determine the IP address of the receiver's zone. | none |
| 0xA802 | NAK_SERVER_OFFLINE | The server at the recipient's zone is not answering. Either his server is off-line or there are network problems somewhere between here and there. | none |
The values of these codes are intended to be distinct from the values of all server-to-server action codes and server-to-client acknowledgement codes. Implementors may assume that this will always be the case.