SO_DOCUMENT_SEND_API1 - sender mail address


I am using function module SO_DOCUMENT_SEND_API1 to send mail with excel attachment.But i am getting error 6 when i pass as sender address.

But at the same time I pass sy-user to sender address the mail is sent successfully. Where is the problem.Can't we give generic mail ID while sending mail to externally.

My requirement was to give a constant mail ID as sender irrespective of who ever is sending the mail.