I've used Contact Form 7 Plugin for my website contact form.
Installation, super easy.
Sending email, super easy....but
I had this problem.
I see a response message “Your message was sent successfully” with green border, but I never receive a mail for that.
Which was exactly an FAQ at
Contact Form 7 site.
I know the cause can vary according to your server.
In my case, the reason was
postfix wasn't working.
So I typed the following command, and everything works fine.
sudo /etc/init.d/postfix start
sudo /sbin/chkconfig postfix on