How to know if a PO has been sent to Supplier in SAP?

The Issue

How to know if a PO has been sent to the supplier (list of PO and their status/ which ones need to be processed)

The Solution

For this case, it is not possible to find from any SAP Standard Reports.
However, you can find it if you look through a particular table
Here's what you should do.
1) Go to t-code SE16N or SE11. Either one would do
2) Enter Table name NAST
3) Now at Processing Status (VSTAT) field, enter 1 if you would like to find POs that you have already outputted a message. OR enter 0 if you would like to find POs which you have not outputted a message yet.
4) Optional - You can enter Vendor code under Partner field (PARNR) to narrow down your POs
5) Optional - You can enter PO number under Object Key field (OBJKY). However you would need to include leading zeros if your Purchase Order numbering does not add up to 10 characters.

Source: http://forums.sdn.sap.com/thread.jspa?threadID=1723257&messageID=9262023#9262023