The feedback system on the site is designed to allow authors to choose to accept email from valid email addresses only.
When you send a message to an author who has chosen to refuse anonymous feedback, the system tries to figure out if your email address is still valid and active before it deliver your feedback.
If you haven't verified your address in the last 90 days, or if you're a premier member, since you've subscribed/renewed last time (if it's longer than 90 days), then a message is sent to you for confirmation.
If you send multiple feedback message before you confirm your email address by acting on one message, then for each feedback you send, you receive one confirmation message.
You only need to act on one confirmation message; not each and every one of them.
Alternatively, you can choose to hide feedback boxes that require confirmation, this way you never send a message to an author that refuses anonymous feedback and you never have to confirm your email address.
To turn off those non-anonymous email boxes, go to the feedback email preferences page.