The fight against spam can feel never-ending. Whether it contains potentially dangerous links to scams and malware, or just an avalanche of annoying ads, junk email is never welcome in your inbox – but fortunately, anti-spam technology is always improving.

Blacklists are one of the most effective spam-filtering techniques. By looking at each email address, or the domain or IP address associated with it, and checking it against known sources of spam, blacklists offer a simple way to block unwanted email.

But with spammers constantly switching addresses, domains and IPs, keeping email blacklists up to date can be tough – and this is where Real-time Blackhole Lists, or RBLs, make a huge difference.

What is an RBL?

A Real-time Blackhole List, or Domain Name System-based Blackhole List (DNSBL), is a published list of IP address owners that are known sources of spam. These include computers and networks operated by active spammers as well as systems passively involved with spam, such as internet service providers whose users are known to send spam, or machines that have been hijacked by spammers.

But unlike static email blocklists, RBLs are also dynamic, meaning they’re updated and published on a very regular basis. This way, RBL subscribers have the best information on all the latest known sources of spam, enabling spammers to be identified and blocked even more efficiently.

How does an RBL work?

RBLs are compiled using a variety of means. Reported sources of spam are routinely added on an ongoing basis, and RBLs also use “spam traps” or “honey pots” – mailboxes specifically set up and published to attract spam – to identify new spam sources and add them to the blacklist.

Once RBL subscribers know which IP addresses are associated with spammers, it’s a simple case of blocking them – this usually happens during the SMTP connection phase. By subscribing to an RBL, email recipients can check the connecting IP to see if it’s on the list, then instantly drop the connection without accepting any traffic.

Find out more about spam filtering

At Fasthosts, we’ve recently enhanced the advanced spam filtering options across our range of email products – and this includes strengthening our RBLs with more known sources of junk email. RBLs are managed by us, so you don’t need to worry about implementing them – all you have to do is select your preferred spam filtering settings in your Fasthosts control panel. For more details, see our help article on setting up your mailbox spam filters.

So whether you simply need professional and personalised email hosting for your business, or the powerful functionality of Microsoft Exchange 2019, Fasthosts offers the latest in advanced spam filtering and protection from unwanted messages – all hosted in secure UK data centres with expert technical support available 24/7.