Sync Signed A signed, synchronous receipt is requested from the trading partner for each message. This is automatically selected if you check Non Repudiation of Receipt. An Initiator asks for signed or unsigned sync receipts if it wants to receive the receipts in the same HTTP connection so that it does not have to wait for the receipts to arrive on a separate connection.
Sync Unsigned An unsigned, synchronous receipt is requested from the trading partner for each message.
Async Signed A signed, asynchronous receipt is requested from the trading partner for each message. An Initiator asks for signed or unsigned async receipts if it wants to receive the receipts in a separate HTTP connection. After the Responder gets the document and verifies the content for integrity, it opens a connection back to the Initiator to send out the receipt that was requested.
Async Unsigned An unsigned, asynchronous receipt is requested from the trading partner for each message.