Hi
You can achieve it with standard output. Please, check these notes
SAP Note 454893 - CHECKLISTSD: Sales document output as an e-mail
SAP Note 960088 - FAQ: Sending SD messages externally
Go to NACE and check if there is any requirement (VOFM) working.
Check also in SU01 for the user if email is populated. Check also the email for customer is valid.
I hope this helps you
Regards
Eduardo