You've probably been harassed by spam at one point or another. Not only is it annoying, but it can contain malicious links and viruses that can compromise not just your computer, but your mobile gadget as well.
To stop the spam, you need a good spam filter. SpamDrain is a yearly service you can sign up for. It deletes spam before it even reaches your inbox. It's a cloud-based affair, so you can use it with multiple devices. You can also set it up to monitor multiple accounts.
Cost: Free; subscriptions are $15 (basic) and $30 (plus) per year