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Blocked Prefixes and Email Deliverability: What Marketers Should Know

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by: Jeff Dellapina (@IBMforMarketing)
29 May 2014

“Why can’t I send to certain mailboxes regardless of the domain?”

Clients having difficulty getting messages delivered to addresses such as “,” “” or “” often ask our deliverability team this question.

The problem is that while these addresses may be valid in certain circumstances, they’re frequently used as spam traps.

Let’s take a look at why this is the case, what you need to know as an email marketer, and how you can best navigate these issues.

Generic Prefixes: Why They’re Bad

As email started to grow, unscrupulous businesses began blindly sending messages to generic email addresses in an attempt to grow their lists. In particular, these companies targeted certain prefixes -- the text on the left side of the “@” symbol of the email address – that often didn’t belong to individuals.

For example, they would send blind mailings to addresses such as in the hope of reaching any live person to get their foot in the door. But they didn’t have a specific user they were trying to reach – much less a relationship with that person or permission to email them.

How This Impacts Email Marketers

As this unsavory practice became more prevalent, receiving companies started blocking any mail sent to those generic addresses knowing they weren’t “real.” And as more and more companies started to block those prefixes, the industry decided to use these default addresses to catch spammers. Subsequently, ISPs began assigning certain generic prefixes as spam traps.

As a result, ESPs today are proactively blocking generic prefixes like the ones listed above – and others such as “marketing,” “spam,” “root” and “webmaster” – to prevent clients from getting into trouble. These prefixes can even be blocked in different languages.  

To help keep your deliverability strong, we recommend you go through your data and remove those addresses that use prefixes that are commonly blocked.

Exceptions to the Rule

There may be times when you have real customers or prospects who opt in to your email program using an address with a blocked prefix. Obviously, these messages need to be delivered. So what can you do?

The good news is that most ESPs will allow you to send to specific prefixes or allow you to remove those blocked prefixes so those messages can be delivered. Work with your ESP to ensure your messages reach these exceptions to the rule without harming your standing with ISPs.

More Deliverability Blogs:

1) “How Do Spam Traps Work? Tips for Avoiding Your Worst Marketing Nightmare

2) “Why NOT to Resend to Email Addresses from Suppression Lists

3) “Feedback Loops: What They Are and What They Tell You About Your Email Program



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