Backup transport in a BizTalk send port
Through the BizTalk Administration Console (or the BizTalk Explorer in 2004) it is possible to configure a send port to deliver messages to their destination.
For each send port you can set the transport configuration which determine which adapter will be used (and its adpater specific configuration).
you also configure the retry policy required and the send handler to use (which depends on the adapter you select).
Through the send port configuration you can also configure a backup transport to use in cases where the primary transport falied.
The process is something like this -
BizTalk tries to deliver message based on the Primary Transport settings.
Failure to trasmit will cause event 5743 to be written to the event log and, if retry is configured for the primary transport, the message will be retried n time (based on this configuration).
If all the retry attempts failed, and a backup transport is configured, event 5742 will be logged to the event log and BizTalk will try to deliver the message using the Backup Transport.
It is important to note that the backup transport is totally independant in terms of adapter configuration, its retries policy (you can have retries on the backup transport as well as on the primary transport, and they can differ) and even the send handler used (which makes sense if you'll can use different adapters).
Also note that there is no time delay between the failure of the last retry attempt of the primary transport and the first attempt to deliver to the backup transport.
you cannot, however, use alternative pipeline (as the pipeline has already been executed at this point)