A Beginner’s Guide To Spam Filters

It probably wouldn’t surprise you to hear that the majority of emails sent every day are spam. From unsolicited marketing messages to emails containing harmful attachments, unwanted junk mail is kept out of our inboxes by dedicated filters that scan and categorise incoming messages. Without them, our inboxes would be far busier – and way more frustrating…

A spam filter is an ever-evolving algorithm, rather like the ones used by search engines to rank websites. It scans every incoming message, and any attachments. It then makes a series of decisions about whether the message was intended for that recipient, if any attached files might be harmful, and whether the message body contains words or phrases commonly associated with junk email. When spammers began misspelling common words in the Noughties, filters evolved to identify word patterns as well as exact term matches.

The threat is real

There’s a tendency to assume spam is fairly innocuous, merely offering us cheap watches or prescription drugs. However, many unwanted messages are designed to do much more than this. Spam often carries harmful attachments designed to monitor keystrokes, or bury malicious software (Trojans and malware) in our devices. These enable criminals to defraud us by accessing our social media accounts and online banking portals. Other attachments recruit devices into huge networks, redirecting processing power and bandwidth towards mass activities like crashing computer servers or distributing spam.

Sadly, even the best spam filters aren’t 100% successful in identifying threats. As algorithms become more sophisticated, so spammers have upped their game. An email sent to five thousand recipients all at once will raise a red flag to any filter, whereas five thousand emails sent to one recipient at random intervals will be harder to identify. Words are commonly misspelled or substituted – we interpret “cheap watch” and “cheep timepiece” as having a similar message, but an algorithm wouldn’t necessarily do the same.

As well as allowing unwanted messages to slip through, spam filters occasionally trap entirely legitimate correspondence. This is known as a false positive. Genuine messages might be sent to a Junk folder in an email or webmail package, or even get deleted before the recipient has any opportunity to view them. Messages vanishing in cyberspace represent one of the biggest problems with email nowadays. The sender has no idea an email wasn’t received, and the recipient has no idea it was sent.

The adjustment bureau

To try and prevent this scenario, modern spam filters have adjustable settings and various failsafes. A message with a potentially harmful attachment can be quarantined – that is, set aside with its attachments disabled until the user makes a decision about its legitimacy. Messages from existing contacts may be whitelisted (always allowed through) or blacklisted (always prevented), and embedded email images could be blocked until the recipient permits them to be shown. Most filters allow users to customise rules according to their business needs – a second-hand watch retailer might want to know about cheap watches, for instance.

Any reputable email provider will have spam filters integrated into its service. As well as running the hugely popular Gmail platform, Google hosts proprietary email accounts for companies and individuals alike. As you’d expect from the world’s leading search engine, its algorithms are very sophisticated with a claimed 99.9% success rate at blocking spam or phishing emails (designed to capture personal data by tricking us). Considering around 60% of email sent every day is spam, that’s an impressive hit rate.

However, it’s also possible to install a spam blocker onto a local network or private computer. This will perform a similar job to Google’s in-house servers, with varying degrees of complexity and scope for adjustment. Leading packages include SPAMfighter, MailWasher Pro and ChoiceMail. Inexpensive and easy to install, these filters block threats long before they reach their destinations.

Market forces

This is great if your primary concern is to keep your company’s inboxes free of malware and viruses. But what if your business depends on email marketing? This is a burgeoning industry, despite the threats posed by global spam volumes. Sending large volumes of email correspondence to unwitting audiences could see your email account being marked as spam in user inboxes, generating abuse reports for the recipient’s email provider or package. If a number of people mark a message as spam, the sender can end up on an international blacklist and struggle to distribute messages in future.

To avoid such an eventuality, it’s advisable to send emails to one person at a time. Use your own database of opt-in customers and contacts, but never rely on bought-in lists where people haven’t signed up to hear from your specific firm. Prominently position a one-click Unsubscribe link in the email, avoid attachments or multimedia files, and never use words like “cheap”…