Just a little bit of background, I used Vijaya Lakshmi's smartform driver that replicated the contents of the standard sapscript driver SAPFM06P (see [Printing Purchase Order from ME9F using custom program and smartform; and [http://vjkvijaya.blogspot.com/2009/03/puchace-order-smartform-driver-program.html]). But it does not send the email so I examined the code of the standard driver.
External Output (email) has a medium (TNAPR-NACHA) of 5. I searched for the text "nacha" in SAPFM06P and It's inside the subroutine adobe_print_output (in include FM06PE04). It also shows there how adobe forms are emailed. This subroutine is only called in adobe_entry_neu (in include FM06PE03). For the entry subroutine of MEDRUCK, entry_neu, only calls to 2 functions are there: ME_READ_PO_FOR_PRINTING, and ME_PRINT_PO.
Now, the question: How does SAPFM06P handle the NEU medium 5 for emails? (especially also the queueing in transaction SCOT)
I tried replacing ENTRY_NEU with ADOBE_ENTRY_NEU in transaction NACE but this actually is for Adobe forms (of which I am not familiar) and since there is no corresponding adobe form, i had an error.
I tried examining the function ME_PRINT_PO but I mostly see sapscript calls (open_form, write_form, close_form). Although I haven't dug deep enough into this rabbit hole, I feel that the email handling is not here, though I am not certain as well.
Any insights that would point me in the right direction will be appreciated.