Hi Amine ,
Emails are submitted to be sent to outside world by the FM SO_NEW_DOCUMENT_SEND_API1 but they are sent by program rsconn01 to outside world which is scheduled in the system .
Time to send the email depends on how frequent the program rsconn01 is scheduled.
To take care of this , take Abdul's suggestion and submit the program after executing the FM for sending email .
Thanks
Manik