This wiki site describes the standard system behavior, when vendor output medium is changed, and how the Output Medium determination is working when Purchase Order is ordered.
Vendor output medium is changed. PO documents exist, that had been ordered and sent to a vendor. The output medium of the old POs will not change upon the change in the vendor master, even if the purchaser creates a new change version.
In this scenario a PO is opened for editing. We will continue to use the 'Output Medium' that was used the last time the PO was ordered. We cannot change the output medium to default every time the PO is opened for editing, as this can be changed by the user when the PO was previously ordered.
Kindly see the screen shots showing the above scenario.
Picture 1 - Purchase order in status 'ordered' and the output set for 'XML'.
Picture 2 - Changing the Output Medium of the vendor to 'Mail'.
Picture 3 - Purchase Order in 'In process' status and the Output does NOT change to Email.
The output parameters are saved with the document GUID in separate table bbp_out_params. This is the reason, the document is not updated, if the default output for the specific vendor is changed. If the vendor default output is changed, the change version of the PO will also contain the old output parameters. This can be changed by removing and re-adding the vendor.
Exception SAP Note to change the behavior
There is an exception SAP Note 2066055 to change this behavior, using a BADI BBP_OUTPUT_MED_CHANGE. Kindly read the Note to understand the solution.
Related SAP Notes/KBAs
SAP Note: 2066055 Output Language and Medium Determination BAdI BBP_OUTPUT_MED_CHANGE