You can send a copy of the mail to the sender using Contact Form 7. If you require their email use the second mail option and then put the name tag exp: [example-tag] that you used in creating the form in the receiver part of the mail.
Here are some screen shots below to illustrate what i mean:
Here is your basic Contact Form 7 form. You will notice that there is a input for email that i have. [email* your-email]
Next here is the email that you will receive. With the tag [your-email]
Now you want to send a secondary email to the submitter. Right below the first set of mail you have a check box that says Mail2. Check it.
You will get this:
In the To: area put in the tag [your-email or whatever you used to call your email input box.
It will now send a message to both you and a mail to your submitter. Don’t forget to put a message in the box next to the other input fields and the other tags as well.