General help

Well, Amazon is a different world. Have never been there and don't understand the support page you've linked. In the Moodle world nothing in the SMTP hosts means that Moodle hands over the e-mails to port 25 of localhost. If Moodle reports success, it means there's a SMTP deamon running at port 25 of localhost and it accepted the mail. What happened in the next leg can be found in the log file of that SMTP daemon. As Moodle suggests at the bottom of the page look for /var/log/maillog, /var/log/mail.log, etc. and search for the target address. Alternatively have a live log 'tail -f /path/to/the/maillog' running in a shell, when Moodle sends a mail.