Spam is the bane of all email providers' existence, so most of them use a variety of methods to block mail. If that's the case, your spam report is probably processed to improve the accuracy of all those methods.
For content filters, your message is processed for:
- URLs and email addresses - these can't change, or they won't work. They're very popular to filter on.
- Checksums - the whole message is processed down into a short string. This works because many pieces of spam are identical, and are sent millions of times.
- words and phrases - one of the more unreliable methods, but still used.
- it's infected with a virus.
- it hasn't been properly secured, and someone is taking advantage of it.
- it's owned by a spammer.
- A mailing list they subscribed to, but don't want to be on anymore.
- A message from a friend that they didn't want to receive.
- As an alternative to the Delete button. (At least, that's the only thing I can assume, seeing some of the messages that people have submitted as spam. Maybe they're just from people they really hate.)
If the message was sent by a legitimate email provider, they'll let you know that an anonymous someone reported a message as spam, and show you the message so that you can take action to prevent these messages from being sent in the future.
If you don't prevent it from being sent in the future, or they don't know who you are, they treat you like a spammer. This means they treat all the mail coming from that computer like it's probably spam.
I know the conventional wisdom is, "Never try to unsubscribe from spam." That is true. However, it is not only OK, but you should try to unsubscribe from lists from legitimate companies and/or providers that you've subscribed to in the past, but don't want to receive anymore. Companies like the Gap, American Airlines, Expedia, etc., are more than happy to remove you from their email lists -- they don't want their messages treated like spam, so they want to make sure that only people who want to receive them do!
When your friend is CCing you on mail you don't want to receive anymore, just tell them, "I'm really trying to get my email under control. Would you mind leaving me off your joke of the hour messages from now on?" And if they won't? Well, delete is always available, too (unless you think your friend really has crossed over into the realm of spamming.) If you are a Pobox Plus or Mailstore user, you can use email filters to automatically send messages matching "Joke of the Hour" to the Spam section. And most email programs will also let you set up filters that will automatically move messages from your Inbox to another folder, or the trash.
What should you do if you accidentally report a legitimate message as spam? Most ISPs are looking for multiple reports, so don't worry too much about any one message. But, if you accidentally selected 20 messages in your mailbox, and instead of clicking Move to store them in your "all-time greatest messages" folder, you accidentally hit "This is spam." instead, well... you might want to shoot an email off to your ISP's customer support, to let them know that your friends aren't really spammers.
The New York Times suggests a list of 10 questions we should all ask our mothers this Mother's Day. Let me suggest one more: "Mom, is there anything I can help you out with for your computer or cell phone?"