Real Magnet

Spring Cleaning the Hard Bounces From Your Email List

Spring is as good a time as any to clean your email list. Going through your hard bounces to determine which addresses to suppress, recover or continue to monitor is something email marketers should do minimally once per year. If you have a significant volume of hard bounces or if much of your email volume is to rented lists or other names of unknown provenance, list hygiene should be performed semi-annually or quarterly.

Why email list cleaning is important

List hygiene impacts deliverability, or rather, a dirty list inhibits deliverability. There are several different types of bounces – some temporary (or “soft”) and some permanent (“hard”). They each mean something different and are read in different ways by ISPs and email administrators, but the underlying message for each is the same: a bounce suggests that an email marketer is trying to reach a mailbox that may not be expecting a message from this particular sender. Sometimes this is because of a technology hiccup (like a full mailbox or a mail server temporarily off-line). Other times it is an error (a typo in the email address, for example). Some bounces are simply the result of changed circumstances, such as a domain no longer existing or a user at a domain leaving the company. But in all cases the mail does not get through, which can compromise your sender reputation to some degree, making it harder for some of your other messages to land squarely in the inbox. Because they are permanent errors, there is no reason to continue mailing to them with the hope that mail will eventually make it through – it won’t.

What the different bounce types tell you

The most critical bounce types to pay attention to are Hard Bounces. Real Magnet classifies these into three different categories. Here is an explanation of each, some reasons why you may see them, and what action to take:

Bad Domain: A bad domain bounce means that the domain within the email address you have sent to does not exist. In some cases, this is from a subscriber who fat-fingered the signup process, and typed “” instead of “” or made some other typo. Other times it is from a domain that no longer exists, the result of a merger or simply going out of business. Bad Domains are also simply made up, such as when someone is required to enter an email address in order to download a whitepaper but does not actually want any follow-up email. Bad Domains are very common in list purchases, as often the lists are quite old and contain extinct domains.

Bad Domain bounces are easy to triage and manage. To start, go through your list of Bad Domains and look for obvious typos (like a “.cm” address instead of “.com”). Fix these and try leaving them in your list until your next cleaning. Look also for domains that you know no longer exist, such as free email providers that have gone out of business, or companies that no longer exist. Go ahead and suppress those – there is nobody home and no amount of ringing the bell will cause the door to open. Finally, other addresses with Bad Domains that you cannot immediately identify, but that have been unresponsive for some time, should simply be suppressed.

A Bad Domain bounce resulting from a company merger. After a month of transition (showing up as Generic Soft bounces here), the old domain finally went offline, resulting in Bad Domains. (Click to enlarge.)

User Not Found: With these bounces, the domain exists but the user at the domain does not. For example, exists as a domain, but if you mail to you will get a User Not Found bounce, as Mr. The Pooh left Real Magnet to pursue other opportunities and spend more time with his family over a year ago. List appending is another cause of User Not Found bounces, which occurs when you (or someone from whom you have purchased a list) see a name like on your list and make (inaccurate) assumptions of other email addresses that may be on the same list, such as (who actually goes by just It is also not unthinkable that list sellers would simply make up names at an existing domain in order to have more to sell.

User Not Found bounces are the most toxic to deliverability, as each one sends a message to an ISP or an email administrator at a domain you would like to reach (and at which you likely have other contacts) that you are emailing a non-existent address. Real Magnet employs an Auto Suppression on some User Not Found Bounces: if an address receives a User Not Found hard bounce two consecutive times within 30 days, with no intervening success within those bounces, our application will automatically suppress the name. If you mail less frequently than every 30 days, however, you should inspect your User Not Found bounces regularly for recurring failures and suppress them.

This User Not Found bounce was the second one in the past 30 days, with no intervening success. Real Magnet will automatically suppress this name. (Click to enlarge.)

Generic Hard: These bounces do not fit neatly into either other classification, either because they are a little different or because the ISP or email administrator that returned the bounce has its own name for it. Bad data is a common culprit. If an import is bungled and multiple email addresses are strung together into a single field (which happens more frequently than you would think),  Generic Hard bounce will occur. Many Generic Hard are also actually Bad Domains, resulting from typos that makes them unreadable and un-proccessable.

Unlike User Not Found bounces, many Generic Hard are recoverable. Go through your Generic Hard and you may well find the errors I’ve cited here – multiple email addresses in a single field, typos, and other obvious data entry or import errors. You can fix these, and re-introduce the correct email addresses into your database. Not only will this improve your deliverability by stripping out bounces, but you’ve just added new names to your list.


Until next time, stay relevant, stay engaged, and get delivered!