Like the junk mail that's pushed through your letterbox, spam email is worthless information that you haven't asked to receive.
What isn't spam is a marketing email you might get from a reputable company such as BT (firstname.lastname@example.org), a utility company or retailer. Although you might not want it, it's legitimate marketing info. And it should come with an "unsubscribe" option so you can remove yourself from the distribution list.
But you should never "unsubscribe" from a spam email as this only confirms your email address is valid and you'll get even more spam.
Some scammers use messages that look like they are from a genuine company and many use our email@example.com email address to try to trick you into giving out private information like your BT ID username and password. This is known as phishing. Remember BT will never ask you to click on a link to confirm any personal detail.
If the email asks you to do this, hover your cursor (but don't click) over the link to see where it should take you. These links can be forged or seem very similar to the proper address but even a single character's difference means a different website. Never click on any links in a suspicious email
Unsubscribe - If you know the sender (BT or if it's a utility company or major retailer for example) you can safely use any "unsubscribe" option. These will often be found towards the end of the email. All EU businesses are obliged to honour your request to be taken off their distribution list.
Opt out - When you register with a site, or put in your email address, make sure you read the marketing small print to see if you're also agreeing to being sent emails. If you're not interested, look for a way of opting out
Use another email address - When signing up for a website that you don't yet trust, why not use one of your additional ten sub-accounts if you've got one spare.
Top tips to deal with spam
Never 'unsubscribe' to spam - This tells the spammer your email address is genuine and you'll probably get more spam
Never reply to spam - Again, you'll be letting the spammer know your email address is genuine and will probably receive even more spam
Turn off images - If an email has images, spammers can tell when you've opened it and this confirms to them that your email address is active
Don't publish your email address in forums or website - Spammers will trawl the web with 'robots' to gather anything that looks like an email address to add to their spamming lists
Check the sending email address - Some spammers pose as legitimate business, so check the email address they are sending from by hovering your mouse over their email address name
Never click on any links or provide personal information in a suspicious email
Use the webmail 'Spam' button - This will send a report into our anti-spam engine, refining the rules for the future, it will also move the mail to the spam folder for you