
Various tools are available should errors occur:
For outbound messages you can check with routing tests, whether the error is located in the determination of the node using the recipient address.
You can Set a Trace for ingoing and/or outgoing messages.
You can analyze the messages sent according to their current status. For example, you can display and resend all documents with transmission errors.
For troubleshooting, you can display the MIME Version of a Document.
You can find further utilities for analyzing an error in the menu of transaction SOADM.
Also note section Send Request Overview.