Miniform did never sent confirmation mails to the visitor filling the form.
There were several reasons for this:
1. The way forms are created makes it impossible for the module to be sure what field data should be used for sending the confirmation. There can be no email fields at all, but you could also create a form with 25 email addresses to be filled. Miniform just does not know what fields are used, and therefore cannot choose where to send a confirmation mail.
2. Spam-protection-rules. Forms could be used for spamming others by using someone elses email address as sender. Those addresses could receive email from your website they never visited. Complaints to anti-spam organisations are very likely to happen causing your website/server to be listed in one or more spam-blacklists.
So, apart for the possible legal issues with automated sending of email without permission it will risk your mailservers reputation.
3. Spam honeypots. If your competition wants to make life difficult for you, they could simply send a couple of forms to anti-spam honeypot addresses. This would instantly blacklist your mailserver, including the email services of all other websites on your shared hosting.
From version 0.12 there is an option to send confirmation mails, but only to registerred - and logged-in - users of your website.
The confirmation email will be sent only to the known address and will not be taken from the formdata.