It depends on your definition of guaranteed delivery.
It you require guaranteed, once and only once ordered delivery then you need to use a protocol that supports this i.e. MSMQ, MQSeries and in the future WCF.
The other adapters provide a level of acknowledgement. And will retry a number of times to deliver the message and provide ACK/NACK messages if you use [b:3f5eb3bdaa]Delivery Notification[/b:3f5eb3bdaa] from an orchestration or suspend the message if you don’t.
The HTTP adapter requires a 200 response from the remote Web server, The FILE adapter needs to successfully write the file to a disk. The SMTP adapter only needs to send the message to the first SMTP gateway server.
You can also layer other protocols on top of the transport to provide acknowledgement e.g. BTF, AS2. ebXML etc.