A spam filter is one of the best ways to reduce email spam risk; however regardless of whether you choose this important email security measure, there are a number of steps you can take to reduce email spam risk, keep your devices protected, and your valuable data out of the hands of spammers and scammers.
11 Spam Filtering Essentials to Reduce Network Security Risk
Listed below are 11 spam filtering essentials that you can implement to reduce spam volume and the risk of cyber attacks.
1. A Real-Time Block List (RBL) is essential
Spam is commonly sent from a known spam server – one that has been blacklisted, or is known to be used by email spammers. Using a Real-time Block List (RBL) is one of the best protections, that will prevent malicious emails from being delivered to inboxes. This one email security feature has been shown to reduce spam email delivery by 70–90%, and it only takes a few minutes to implement.
Even if you use a spam filter this measure is important. It will reduce the load on your spam filter, email server, and network. An RBL works by blocking messages before they are downloaded, which will also help to save bandwidth. There are a number of ways to do this, although zen.spamhaus.org is one of the best. It is widely regarded as being the best at spam blocking, is updated frequently and importantly boasts a very low false-positive rate.
2. Recipient Verification will block spam sent to invalid email addresses
Spammers like to bombard companies with emails in the hope that some will get through, or that a catch-all is in place and all will be delivered. Common email addresses used are webmaster@, info@, admin@, sales@ etc. etc. These email addresses are commonly used by companies and there is a good chance that they will be delivered to someone. However, you can use Recipient Verification (RV) to reject the bulk of these emails, and only have properly addressed emails delivered.
To do this, use Microsoft Active Directory integration or upload a CSV file of valid email addresses to your spam filter and mail server. This technique will prevent speculative emails from being downloaded and will similarly reduce the load on your spam filter and mail server, and save bandwidth. This method of spam prevention will take longer to complete than setting up your RBL, but it is a worthwhile investment of your time as it will result in a major reduction in spam delivery.
3. Configure your server to require correct SMTP handshake protocols
This is one of the most effective methods of blocking spambots and it will stop the majority of spambot emails from being downloaded and delivered. This is a fairly quick task to complete, and should only take you a few minutes. You will need to set your configuration to require a HELO (EHLO) with a Fully Qualified Domain Name. However, it is important to note that it may be necessary to add some of your suppliers to a whitelist to ensure that their messages do not also get blocked. Not all of your suppliers and contacts will have their own email servers configured correctly, so genuine emails may be caught and blocked. Individual organizations will find this step particularly beneficial. MSPs less so, or not at all.
By using the above three spam prevention methods – which incidentally can be used on virtually all email servers – you will make a considerable bandwidth saving, and dramatically reduce the number of spam emails that are downloaded. This will also help to protect your network from malware. If you allocate just 30 minutes to do all three, it will save weeks of your time, which can be better spent on other cybersecurity tasks.
4. Regularly scan for viruses
A basic security measure is use is a robust and powerful anti-virus program, regardless of whether you use spam filtering. If you don’t implement spam filtering, this measure is especially important, as you are more likely to have viruses delivered to email inboxes.
Even with spam filtering in place, it is also important to have anti-virus software installed and, of course, AV engine and virus definitions need to be kept up to date. Software should be configured to update definitions automatically.
With spam filtering in place, it should be possible to stipulate the update frequency. Be aware that a different anti-virus can be employed to protect endpoints. Using the same AV engine for mail servers and endpoints means that if for any reason your AV software does not detect a virus, all endpoints could potentially be affected. By using a different AV engine for endpoints and mail servers, you maximize the probability of a virus being detected. Fortunately, competition is fierce in this market, so you should not have to pay top dollar to have two different engines in use.
The following steps will apply if you have a spam filter. These will apply no matter which spam filter is used, be that open source, commercial or even cloud-based spam filtering.
5. Certain attachments carry higher risks so block them!
Executable files – those with a .exe suffix – are particularly risky. Fortunately, it is not necessary to run the risk of a user double clicking on them. The best option is to block these file types and other risky file types if they are not typically needed by staff members. Be aware that spammers are sneaky. It is common knowledge that .exe files are risky, so they mask them with other extensions: PDF, XLS, DOC files for example. To counter this, block by MIME type, not by file extension.
6. Take Action to Block Phishing Emails
Phishing emails can easily fool employees into clicking on links that direct them to URLs loaded with malware. There are a number of URLs that are recognized as phishing websites and it is possible to block these quickly and easily. To do this, use SURBL and URIBL lists to check for website domains that frequently appear in unsolicited emails.
7. Ensure that your spam pattern library is regularly updated
You may find that your spam pattern library cannot be configured manually, as this may be hard-wired into your spam filter. Spam signatures are based on a huge database containing recently added spam, as well as past signatures, with the spam-fighting community adding to the database on a daily basis. There are many different resources that can be used, although if you want to ensure you have a fully up to date database of spam signatures, SpamAssassin is arguably the best choice.
8. Bayesian filtering will recognize more spam and block less ham
A Bayes engine is used by most spam filtering engines and can be trained to recognize spam, and differentiate it from ham (i.e. not spam). It is therefore important to use a regularly updated spam pattern library, which will assign incoming emails with a score, in addition to using feedback provided by end users. The Bayes engine learns what is spam and what is not, and will apply the lessons learned to new emails that are received, constantly improving its detection rates to ensure all spam is caught, and false positives are reduced.
9. Stipulate the spam score that is right for your company
As a system administrator you have the power to decide what spam score is right for your company. This will depend on how much risk you want to take. You will find that spam filters will usually allow you to dictate how aggressive they are, although you may find this requires a certain degree of tweaking to ensure that spam doesn’t get through and ham doesn’t get accidently blocked. A spam score is assigned by a number of factors, although the type of attachments and the email content are the two main ways that the spam score is calculated. This process is not particularly time consuming, but bear in mind that the first two weeks after your spam filter has been installed is when this task will need to be completed. Be sure to use your trial period to tweak your spam filter to ensure that spam is blocked and the number of false positives are kept to a minimum.
10. Get your end users working for you
Your spam filter will not always get things right, and some spam and junk emails will slip through the net from time to time. It is therefore useful to instruct end users to manually mark any spam and junk emails received, should they get delivered to their inboxes. End users can help to train your Bayes engine to recognize new spam emails and correct false positives.
11. Provide email security awareness training to employees
Nowadays it is essential that all staff members receive security awareness training. They must be taught how to identify spam emails, phishing campaigns, and potential viruses. They must also be informed of the correct actions to take if they do discover a phishing scam or suspect that an email may contain malware or a virus. Also instruct them on the correct actions to take if they do accidentally open a suspicious attachment.
Is it the job of a system administrator to train employees how to protect themselves and their computers? Arguably it is not, but it can save a lot of headaches down the line. Even a little training can go a very long way. Unfortunately, this is an area of email security that is all too often forgotten.
What is essential, is that employees are aware of the risks of falling for a phishing campaign or downloading malware. In some cases, it could spell the end of a company, and along with it, their jobs. You can always use CryptoLocker to scare employees into paying attention.
Training could well make all the difference. Besides, if you do provide training and employees still take risky actions and infect the network, you will have a clean conscience and can say it is not my fault! And be justified in saying it.