I built a contact form for one of my clients that used FormMail and ReCaptcha. Everything was working fine when they decided to move hosting providers. The new hosting provider has much stricter rules for their web servers in that IP adresses need to be specified in the control panel to allow outgoing connections.

As soon as we moved the files to the new web space, ReCaptcha failed with "Could Not Open Socket". Unfortunatelly I could not register the IP adress since Google owns several thousands of them. And the control panel did not allow domain or port entries, strictly IP numbers.

I ended up removing the ReCaptcha and enabling FormMail's built-in captcha function. The images are not as pretty, but it works.