Never “unsubscribe” to an email that you didn’t subscribe to in the first place. Always “block”. If the spam came from a random or outdated list, unsubscribing will only confirm to the spammer that your address is “active”.
How did they get your email? One source could be from someone you know. If they were careless and allowed their computer to become infected by a “bot”, it could have collected all the email addresses in their address book and that would include yours.
Remember the best offense is a good defense, and your best defense against spam and junk email is to employ “alias” addresses. An alias works like forwarding. Everything sent to the alias comes to your regular email inbox. Use alias addresses to subscribe to things you want to subscribe to. Hosted email (email provided by your web site host) often include the option for alias addresses. Free email providers, like Gmail, also provide for free alias email addresses. Simply create several email aliases and use them when you want to subscribe to newsletters, “special offers” or the next Publisher’s Clearing House drawing. Then simply retire the aliases that generate the most spam and junk. An alias is also secure, because will an alias can be used to RECEIVE messages, it can’t be used to send because there is no password for an email alias address
You will find that many free “services” you subscribe to will sell your email address, and that includes such unlikely sources as Gmail, YouTube and Yahoo. How do you think they support all those “free” services? Always remember that when something is free, it’s likely that YOU are the product being sold.