Add a subscribe/sign-up checkbox to Contact Form 7 plugin forms.
You can use the Newsletters – Contact Form 7 Subscribers extension plugin by Tribulant Software to do just that!
It is a free extension plugin but the Newsletter plugin itself is premium. You can try out the Newsletter plugin LITE version though! The extension works with the LITE version too, no problem.
Capture email/newsletter subscribers from your Contact Form 7 plugin forms into the popular Newsletter plugin.