Do we have a global unsub / global opt out concept (subscribers who don't want to receive any communication at all) in adobe campaign ? If yes, how and where we can access to these data? It's different to the Services and subscriptions function
There is an attribute in nms:recipient schema named @blacklist which can be set to true or Yes if you wish that the recipient is never sent a communication, even by mistake.
Delivery templates have a default exclusion criteria to remove such recipients from targeted audience. Adobe Campaign adds it by default on every new template but a marketer can disable this option as well and hence please do revisit all the delivery templates.
So, if you have a data file with the list of emails that should never be sent an email, please create a workflow to update corresponding recipient's blacklist field to true.
If you wish to provide this feature on a webApp, you will have to write custom JS code to update the recipient record.