Where does the list come from? After the junk mail is filtered out, Microsoft looks for information in the message header that identifies it as a subscription.
What it does: Subscriptions is list of all senders whose messages contain subscription information in the message. Included is an Unsubscribe button and Outlook.com will try to unsubscribe you. This is great for legitimate subscriptions, such as newsletter or stores you’ve purchased from before.
However, many users discover their subscription list is full of spammers and fake subscriptions. They cannot (and should not) try to unsubscribe from the fake subscriptions. If the link works, it will verify your address is good (which will lead to more spam) and the unsubscribe link may lead to a page full of malware.
Until Microsoft adds a Delete button, users are stuck with the spam subscriptions on their subscriptions list.
Vote for and share your comments in this Uservoice suggestion: Problem with "Manage Subscriptions" & Junk Email