PO message determination

Dear gurus,

I have a problem with my PO output.

I would like to trigger an email to Requestor when Purchaser save PO via t-code ME21N. When I convert PR to PO, it does not auto propose my new ouput type.

In addition, I also would like to know which is the correct partner function as this email is not send to vendor but to internal user.

Thanks in advance!

Regards,

Santthi