Hi Suhel,
The problem in your case is that when you are trying to send the email through external send, the system is generating a printout. Moreover, i guess you must have checked the sost and there is no email. Please once check that the print preview to confirm if there is actually a printout. There is nothing wrong in your config. Please ask your abaper to check the code once again, it is likely that there is a change in recent past and the wrong functional module is getting called. You may recieve the error "output program is not defined" in other combinations.
ABAPer is the key for your resolution in this case
Regards
Vivek Singh