Hi Rohit,
I tried the blind form submit to track the opt outs through system action URL of 'Unsubscribe All'.
I have added this System URL in redirect to webpage processing step but because this URL uses recipient ID which unique to each email address, I can't seem to successfully unsubscribe the contacts. Although I am able to capture the blind form submits and its redirecting to the system landing page if I use any one of the recipient ID.
How can I populate recipient ID for different email addresses?