Email Address Not Found: Email Bounces Explained

How many of us have hit 'send' on an email, only to have an email bounce notification arrive in our Inbox moments later, letting us know that the recipient didn't receive our message? Email bounces are relatively common, but for email marketers who depend on email campaigns to drive leads, it is imperative to understand WHY an email got the boot. In this article, we'll explore bounced email and why it happens.

Synchronous and Asynchronous Email Bounces

There are two forms of email bounces: synchronous and asynchronous. The main difference between the two is how long it takes for the bounce message to be returned. Synchronous email bounces are the ones that instantly send a message back to your Inbox, letting you know about the failed delivery attempt. Asynchronous bounces trickle in after the release of your email campaign, instead of flooding in at one time.

The speed with which emails are bounced has to do with how they're being intercepted. Here's an example: Imagine that your email marketing campaign is being sent through your server at acme.mail.com, relaying the message to inbox.mailbox.com and attempting to be delivered to This e-mail address is being protected from spambots. You need JavaScript enabled to view it. . At the point that the server recognizes the worthless email address, the connection will be aborted, and you'll be notified of the bad email address. This is an example of a synchronous bounce.

An asynchronous email bounce occurs differently. Instead of the connection breaking upon arrival to inbox.mailbox.com, mailbox.com will actually acknowledge your message and attempt to push it through to its in-house address data. Upon realizing that the email address you sent to is not a good one, a bounced email notification will be generated and delivered to you.

Understanding Email Codes

After the email bounce is determined to be synchronous or asynchronous, it is assigned to one of two categories. There are two standard codes used for emails:

• RCF821- simple mail
• RCF1893- enhanced mail

Bounced emails that are sent to a permanently closed inbox can be recognized by the number 5 in the front of the code that is returned. A 550 in the RCF821 and a 5.1.1 in the RCF1893 both have the same meaning, which is that the email address is null and void--in other words, a hard bounce. Bounces of this nature are usually attempted a time or two during a period of a few days, to allow for any temporary system fault that was occurring.

Bounced emails that are considered soft or transient usually have a code with a 4 in the front. This means that your email campaign could not be delivered at that particular moment--but that there is a good chance it will be able to be delivered, and to retry your email later. One of the most common issues that would cause you to receive an email code with a 4 at the front is that the potential recipientâ€