Our Moodle (course management website) has been configured with an email account that can send emails to the students. The created email address is working fine. I mean I can login to the mail server and check the inbox of this user (the moodle). Also, there is a plugin for testing the setting. The log shows that delivery is not allowed and I don't know which side is causing such a problem, either the mail server admin or some setting errors.
Please note that I can login to the web interface of the mail server and send a test message manually by composing an empty message. So, I am pretty sure that the moodle user must send an email.
SERVER -> CLIENT: 235 Authentication successful
CLIENT -> SERVER: MAIL FROM:
SMTP -> get_lines(): $data was ""
SMTP -> get_lines(): $str is "250 Sender accepted
"
SMTP -> get_lines(): $data is "250 Sender accepted
"
SERVER -> CLIENT: 250 Sender accepted
CLIENT -> SERVER: RCPT TO:
SMTP -> get_lines(): $data was ""
SMTP -> get_lines(): $str is "550 Delivery not allowed to
"
SMTP -> get_lines(): $data is "550 Delivery not allowed to
"
SERVER -> CLIENT: 550 Delivery not allowed to
SMTP ERROR: RCPT TO command failed: 550 Delivery not allowed to
CLIENT -> SERVER: QUIT