强制等待发送邮件PHP之间

I am using SwiftMail with Symfony2 to send email with a form. I want to check if the visitor has already send email 5 minute ago.

So I add one attribute 'time' in my class. Before sending email I check if (time + 5 minutes > now)

But the visitor can send a email if he close the broswer and reopen it. I tried to use cookies but that useless because the visitor can clear his cache.

So how can I save the visitor's IP with the time of his last send. I can do that with doctrine. But it's very big operation to do that, no ?

Sorry for my english I am learning it.