Hi Eponce,
We can't reproduce your issue on our development equipment. Our plugin are working properly with last WP version. You can send test mail via our demo site. However, we are using third-party SMTP plugin for mail settings, as recommended in our plugin documentation.
Possible, your issue is hosting-based, so you can ask hosting support about it (ie your email address in a black list, your host doesn't allow to send mail from non-domain email address etc).
Also, you can find good references in the topics that you started for the Contact Form 7 plugin.
We hope this information will help you.
with best regards,
WordPress WebCodin Team.
