When hitting the send button on the contact form of our website   https://www.aks-foodtec.de/kontakt.html

I get the error " This method is not allowed" or the screen below.
Unfortunately, I´ve not found a way yet that the email gets sent out.

Under data management, I´ve selected the "PHP mailer"  (script-type for sending email) and 
tried both the "post" and the "get" option.

I´ve also tried all other script-types for sending emails - none of them worked.

Any suggestions?
The page is hosted at t-online. 

Thanks for your help!