It looks like there is no way to be aware of any leads unsubscribing from the emails powered by Upviral.
As a result we may keep on sending them messages from within our autoresponder system :-(
1) Simple option: Is it possible to have the list of the unsubscribed leads for download so that we can update their status in the autoresponder system? (that's a tedious manual update by exporting/importing a file and systems are not automatically synchronized -> there might be situations where a lead will still be emailed after unsubscribing from Upviral's emails)
2) Better option : Is it possible to be notified through email (a specific admin email address setup for that campaign) everytime a lead unsubscribes so that we can automatically notify the autoresponder system thanks to Zapier (ZAP: gmail -> google spreadsheet -> autoresponder (status update)) ?
For the time being the workaround consists of not using upviral powered emails and rely 100% on the autoresponder. But we are missing out on all the custom fields and social sharing buttons provided by Upviral (except the ref link).