The email/SMTP works in a relay system and there might be multiple relay within Oracle’s network .

The status by itself is not sufficient to proof that the email is delivered to the customer’s email server. The email/SMTP works in a relay system and there might be multiple relay within Oracle’s network before actually handing the message to the customer’s email server as published by DNS. The status OK here just means the message was sent to the first relay server within Oracle’s network. This is not sufficient to provide to our customers that their email system is the issue (either categorizing it as spam or just discard the message).