Mail sent but wothout any success message

Info: I use Contact Form 3.8.3 and WP 4.0

Hello,
I have exactly the same issue posted by zvaranka.
I use: WP 4.0, Contact Form 7 3.9.3 and Really Simple CAPTCHA 1.8
Thanks for your help.

Same here too, ever since WP4 upgrade. No new plug-ins, just wordpress 4 upgrade. I get the spinning wheel, but the contact is already sent, so clients keep trying to send over and over

The spinning arrow is a common symptom of a Javascript conflict with either your current WordPress theme or one of the other plugins you are using – see Contact Form 7 Email Issues – there is a link there that covers Javascript Conflicts.
??
Contact Form 7’s Javascript is not completing due to some problem in some other Javascript loaded on that page.

You can stop Contact Form 7 loading any JavaScript

When the value of WPCF7_LOAD_JS is set to false (default: true), Contact Form 7 does not load the JavaScript. You can set the value of this constant in your wp-config.php like this:

define('WPCF7_LOAD_JS', false);

See https://contactform7.com/loading-javascript-and-stylesheet-only-when-it-is-necessary/

You will lose all of CF7’s Javascript functionality and of course the real cause is the theme or other plugin which I would definately regard as poorly written and avoid using.???

Thanks for the Info. I inserted the

define('WPCF7_LOAD_JS', false);

code into my wp-config.php, but the spinning wheel remained the same.

I have found the solution, I disabled all plugins the I reendabled them one by one checking the form sending. Finally I found the problematic plugin that had casued the problem.