Real Magnet

What You Need to Know About Block Lists Before You’re Blocked

If you’re sending high volumes of e-mail, chances are that you’ll find yourself on a block list sooner or later. The secret to surviving (and correcting) a listing is to be ready before it happens. Here’s what you need to know now, before you find yourself listed.

Stay Cool. No one ever got a listing removed by screaming down a phone line or threatening legal action. Don’t expect (or demand) a good customer service experience from a block list – you are not their customer.

Block Lists Don’t Block Mail. In the initial panic following the discovery of your listing, it’s easy to forget that block lists don’t actually block any mail; it’s your recipients’ mail servers that do all the blocking. The filters used by many ISPs and companies reference data from block list, reputation scoring firms, and especially feedback from their customers to inform their filtering decisions.

Some Block Lists Matter More Than Others. The vast majority of public block lists don’t matter at all. There are plenty of web sites that offer to look up your sending IP on hundreds of lists all at once, but unless you’re listed on one of only about a half-dozen, you probably have nothing to worry about.

So which are the ones worth worrying about? Any of the lists operated by Spamhaus.org, the CBL, URIBL, CloudMark CSI, SpamCop, Barracuda Central, and sometimes SURBL and SORBS. The cast of characters changes a little from time to time, but these are usually the heavy lifters.

Different Lists Do Different Things. A listing on the Spamhaus SBL means something very different from a listing on URIBL, which is entirely different again from a listing on Spamhaus PBL. Only one of these (SBL) is a list of suspected spam sources. The URIBL lists domains that appear in spam. The PBL is a list of IP space from which unauthenticated e-mail is not supposed to be sent. Don’t assume you’ve been listed because someone thinks you’re sending spam; make sure you understand the reason for your listing before you waste time fixing a problem you don’t have.

Many Block Lists are Automated. Some block lists operate with as little human input as possible. The URIBL is a good example. It automatically adds the domains it sees in the links contained in spam, so that users of the list can block mail based on presence of those domains. The good news is that delisting is pretty straightforward – just submit a short request on their web site. But expect the listing to be reinstated automatically if it sees more spam that contains links to the offending domain.

Avoid the Death of A Thousand Cuts. The most dangerous block lists are the private, home-grown lists created and maintained by IT professionals at the companies you’re sending to.  These lists are unpublished, unqueriable, and are controlled by harried mail administrators who don’t have time to check every few weeks to see if it’s okay to delist you..

Imagine a temp firm that specializes in the placement of legal secretaries with medium and small law offices. They may not be sending a lot in overall volume, but if the temp firm is listed by just a few of their target customers, the impact on deliverability will be noticeable. Once they’re on one of these lists, the affect is very localized, but very difficult to reverse. As the number of listings at individual law offices grows, the temp firm may find their target market is all but inaccessible to them via the e-mail channel.

Ironically, one of the benefits to senders of the large, centralized block lists is that it takes just one delisting to get mail unblocked across great swathes of the Internet. It’s a lot easier than contacting every domain you send to, one by one.

Block lists seem a lot less scary once you understand how they’re assembled and used. If you find yourself listed, keep calm, find out why, and gather the data together you need to fix it. At Real Magnet, we have deliverability professionals ready to manage the process for you, and even help prevent a listing in the first place.

Andrew Barrett is Sr. Director, ISP Relations & Deliverability at Real Magnet.