I am appreciated for your reply. According to your advice, I re-configured the SMTP setting on Moodle server, and purged all caches. This time SMTP connection is successful, but I didn't receive the notification email.
I received a success message after doing the eMail test on Moodle server:
I also got a success message after registration:
Mail tracking logs:
The log entry
stat=Sent ( <remote-id> Queued mail for delivery)
indicates that the remote server accepted the message. From the perspective of your SMTP server is has been delivered. It is now in the next hop towards the recipients INBOX.
Typically, the message will move through SPAM and anti-virus filters etc. before ending up either in the recipient's INBOX, Spam folder or possibly silently discarded.
However, there was no notification email in those folders. I registered 3 accounts with 3 different emails, none of them had the notification email (neither in INBOX, nor in spam folder).