widereonline

The mail settings:
To: the mail address to receive the contact form
From: The mail address of the sender of the contact form

I also tried different settings here. All settings give problems.
Other websites I have set up with the same types of settings do not have the error of display

The contact form with the issue can be found on the following page: https://www.hetoudepakhuis.nl/contact/

The website with the problem is: https://www.hetoudepakhuis.nl/