Asyn vs Sync of guaranteed delivery on B2B


I am using the Sync method of guaranteed delivery between two B2B 4.0.1. servers.

I lost messages when using async methods.
Can you tell me how’s different their usages and meanings between sync and async.

Thank you in advance.

Does anyone know any further details on this issue where transactions are “lost” when we use Async Guaranteed Delivery. We are seeing the same problem on our installation and we can’t use sync due to other issues.

b2b version 4.0.1 on Windows 2000 Server.

Any insight will be most helpful!