Immediate and Delayed Bounced Email Events

By: Chris Lewis

Email bounces that occur when you send out email from any email software sending program can occur in two different way:

An Error During Sending - During sending, if your SMTP server deems a certain email address as permanently undeliverable, then your SMTP server will return a 500-series error code which tells Campaign Enterprise or Email Marketing Director to hard bounce that email immediately.  These kind of immediate hard bounces usually only occur for two reasons: The email address was malformed or the mail system you are sending through has "authority" over the domain of the email being sent and can just right on the spot if the email address is good or not. We see this happen a lot with Exchange servers where you both you the Exchange Server for receiving and sending emails.  If your company domain is hosted on the Exchange server then the SMTP server of the Exchange server will only allow valid email addresses to be sent with those domains.

Returned Email - This is the most common way bounces are recorded because most of the time your SMTP server does not have the immediate authority to say whether or not an email address is valid. In this scenario your SMTP server simply relays the email message you sent to the SMTP server that has authority for the domain (from the MX record). When your SMTP server is talking to the target SMTP server, the target SMTP server might say "that email box does not exist" which is a 500 series error.  This triggers your SMTP server to send the email back to you (or your bounce account).  This can take seconds to hours to happen.

So, overall, bounces are somewhat difficult to deal with since they may happen from several different source, and since there is no standard for the formatting of bounces, it become the task of our software to decipher a bounced email which may have all or just part of the original message. In the next article, we will discuss the different ways to deal with the returned emails.