Goal : print PO by send mail
0. set e-mail parameters like in this
System administration > Setup > System > E-mail parameters
1. Set at vendor
General > Print mangement
2. right-click > override
enter email address
3. when print PO, tick use print management
If you are running CU7, you can send to specific vendor email contact using suggestion in msdn.
NOTE : if not using print management ( use Printer setup > Purchase Order ) it will pop outlook program to send mail, not sending from the mail server.