karmeba on "[Plugin: Contact Form 7] E-mail is not arriving"

Hi ,
I downloaded the 3.3.3 contact form 7 in a site I am working with the WP version 3.5.1
The e-mails don't arrive even the form shows the message:
Your message was sent successfully. Thanks.
I have been using this plugin many times

Any suggestion will be welcome.

Thanks in advance,

http://wordpress.org/extend/plugins/contact-form-7/