I learn that it is caused by my hosting provider doesn't support php mail. They advice me to use WP Mail SMTP Plugin. After I activate and set that plugin, WP started to notify new user. But WP Project Manager can't send notification e-mails still.
What I suspect is, the SMTP plugin you are using doesn't support BCC. We are sending each notification as BCC so that anyone doesn't see others email address. But this SMTP plugin isn't picking up those emails, it's just handing the “to” emails.
Mr. Tareq, then there is 2 option:
1. Using an other SMTP plugin which support BCC. Do you know which one supporting that?
2. Edit WP Project Manager plugin to send e-mails as CC. (it is not problem for us)
How can I find that part of code?