How to fix WordPress user registration email not sending while admin notification is sent.

Today I noticed my WordPress is not sending registration email to new user, but I’m received the notification email.
I spent 2 hours to figure it out.

• Local SMTP mail server checked, email sent without any error.
• External SMTP mail server tried, email sent without any error.

Both sending method sent notification to admin only, but not user registration email.

I suspect the problem is not caused by mail server, then I check all  installed plugins.

Finally I found a plugin called “Stop Spammers Spam Control” cause the problem I mentioned above. By deactivating it, everything works like charm again.

Conclusion

So if you having the same problem like me, try deactivate some installed anti-spammer plugins. It might helped.