Contact Form 7 uses the standard recommended method used to send emails in WordPress - wp_mail which is based on the the standard PHP mail() function.
By default, the WordPress mailer fills in the From: field with wordpress@yourdomain.com and the From: name as WordPress. This is fine if this is a valid e-mail address which can be authenticated.
Problems can occur if you set your real email as the From: address in CF7 and it’s something like wpgod@gmail.com. In this case the mail may not send because gmail.com is not a domain handled by the mail server at your particular WordPress install.
A solution used by some people is to simply create a new email address called wordpress@yourdomain.com and use that in the From: address in CF7.
See http://codex.wordpress.org/FAQ_Troubleshooting#E-mailed_passwords_are_not_being_received for a more detailed explanation of the issues involved.