Cousin Domains Are What Spammers Use

Sending low-volume mail from cousin domains has made a comeback, mostly among cold email outfits. The pitch is that it protects your main domain's reputation. Using cousin domains is a terrible practice, and the reason is simple: it's what phishers do, for many of the same reasons.

Cousin domains are built to look like yours

A cousin domain is a domain name designed to look nearly identical to your primary domain. If your domain is example.com, a cousin might be examp1e.com (a numeral one in place of the letter l), exampl3.com (a 3 in place of the e), or examples.com (an added s). The whole point is that a reader, and sometimes a filter, won't notice the difference.

The appeal is evading the systems that protect recipients

Marketers reach for cousin domains for two reasons. Rotating across several domains is supposed to keep any one of them from tripping spam filters on volume or repetition. And if a cousin domain gets blocklisted, the only casualty is the "business development team." Everyone else keeps sending from the main domain without interruption.

Both reasons involve getting around the systems designed to protect recipients. That should tell you most of what you need to know.

You are training your recipients to fall for phishing

Mail from a slightly altered version of your domain looks suspicious because it is. Recipients who notice will treat it as phishing or spam, which means lower engagement, more unsubscribes, and more complaints. Recipients who don't notice are worse off. You have taught them to trust lookalike domains, and the next lookalike they see may belong to someone who isn't you.

Mailbox providers notice too. If you run into a delivery problem that needs a provider's help to resolve, expect a harder conversation, because the people on the other side know a cousin domain used to send unwanted mail was no accident.

Every cousin domain also needs its own DNS, SPF, DKIM, and DMARC setup, and each is another place to make a mistake. The market has noticed. Today, I saw a "cold email enablement" provider offering an add-on service to handle authentication for those extra domains.

There is legal exposure as well. Using lookalike domains to obscure who is actually sending the mail is the kind of deception that invites regulatory attention, on top of damaging your brand.

The domain you already have is the one to protect

None of this protects your reputation. It only spreads the damage around. The alternative is the unglamorous one. Send relevant mail to people who asked for it, authenticate your primary domain, keep your list clean, watch your engagement and complaint data, and follow the law where your recipients live.

You are borrowing a technique from the worst people on the Internet, for the very worst reasons, and the mailbox providers know exactly who taught it to you.