I was assign a print program for PO and what i did for the output type was to send auto PO to user and sender and information.
But what the functional requested more that is when the sender email has received he wants a pop up which is to say email have been sent to you.
So using the FM CALL FUNCTION 'SO_DOCUMENT_SEND_API1'
and any error occured it will pop up in Send Express Information (pop up)

Configuration to be made in Shared office settings
- Tcode :- SO16
- Mail sy. grp
Select No Mail System Group

Purchase order, print program.
Prereq : create print program and config in NACE
When you plan to do some coding after your repeat the output
1. send email to vendor
2. do some coding as soon as you push the output again the codes below are important

    IF nast-nacha = '5'. "EXTERNAL SEND + TCODE + AND WHEN SAVING
      IF ( sy-tcode = 'ME9F'  AND sy-xcode = '9AUS' ) OR
         ( sy-tcode = 'ME21N' AND sy-ucomm EQ space ) OR
         ( sy-tcode = 'ME22N' AND sy-ucomm EQ space ) OR
         ( sy-tcode = 'ME23N' AND sy-ucomm EQ space ) OR
         ( sy-tcode = 'ME28'  AND sy-ucomm EQ space ) OR
         ( sy-tcode = 'ME29N' AND sy-ucomm EQ space ).