No Email sent — Spinning Wheel

Hi Support,

I am a long time Contact Form 7 user and appreciated the Plugin very much — but right now I am pretty unhappy.

I moved my website projects to a Cloud Server and all existing Contact Forms don’t work anymore. The endless Spinning Wheel is standard now. My first guess was a misconfiguration of my mail server. As all other email works fine I have no idea what to do on this side anymore.

It took me hours, no days to investigate all the standard solutions
(including: disabling all Plugins [no change], testing on a default Theme [no change], using an SMTP Test Plugin [it sends emails without any problems], rolling back Contact Form 7 to former releases [no change]).

Of course I double checked all forms for spelling mistakes etc. — the result ist still the same.

Now I decided to test with WPForms, set up a form within minutes with standard options — and everything works fine with this Plugin.

I would like to stick to Contact Form 7 but it seems very unlikely right now. What am I doing wrong?

Cheers, Frank

The page I need help with: [log in to see the link]