avi123- see drewbarden's response above.
I implemented it on all of my contact 7 forms and it has done the trick. Contact form 7 defaults that the "From" email address is from the sender. Many web hosts see email from yahoo, gmail, hotmail and others as spam. If you set it to come from your website like, info@yourwebsite.com, then the forms will work again. You can code the form to capture the senders address in another way.
The only drawback is reply's but you can also code in a "reply to" link that has the senders address.