I’ve set the id option, but it doesn’t work as expected. The id attribute doesn’t appear in HTML.

Please be aware that the id HTML attribute must be unique in the entire document. Having multiple elements sharing an identical id value is invalid in HTML and can lead to unexpected behavior on the browser. Contact Form 7 ignores the id option when it detects that an identical id value has already been used on the same page.

Just another contact form plugin for WordPress. Simple but flexible.