This field is located on the Purchasing header screen. If you set this field to Yes, a hyperlink displays which indicates the Sent Date and Method, which can be changed if you have the security bit to allow Changing a PO (bit 212). The applications that mark a PO as "sent to vendor" and update the Sent Date and Method are:
Electronic PO transmission for all vendors – the Method is set to Transmitted
Purchase Order Report (RPO) run with the new Option F “Final Version for Vendor”
If you use Option F, and have selected to both Fax and Email, the Method is set to FAXed
If you use Option F and have selected to Fax, the Method is set to FAXed
If you use Option F and have selected to Email, the Method is set to E-mailed
If you use Option F, and are just printing, the Method is set to Printed.