User registration by email verification not working.. need help

Hello Warriors, I was trying to integrate phpbb forum on my site…i have set email verification for new registration. but users are not getting verification email.
Not only phpbb but same thing happening with my WordPress blog. While a user tying to register an account on my blog they asked to activate their account by verification link. but actually they are not getting any verification email.
So please tell me the solution… I think i need to change some settings but don’t know where. I want user’s registration via email verification.
Additional information: Wordpress is installed on main domain and phpbb is installed on sub domain