Guests can not use the contact form - Error while sending e-mail

[danijan]

I have installed the Plugin and it works fine for Users, that are logged in, but
Guests see the Contac form on the website and they can fill in, but when they try to send it comes the Message: "Error while sending e-mail"

Here you can see the error message

The Box "Allow guestts to see the form" is activated in the plugin

I have tried on another page, where i have the same problem.

Thanks for helping

[jacceko]

Two years zero reaction -
I have the same problem in 11.5, Is some hope for solution??