Email Marketing Message Bounce Back – What the SMTP Error Code Means

When you send your email marketing messages, are you ever alarmed by SMTP error codes?

What are these email error codes and what do they mean? Should it be a cause for alarm or can it be addressed by a simple quick fix?

Before panic sets in, first let’s understand these codes and what they mean to your email marketing program. Otherwise known as Simple Mail Transfer Protocol, SMTP is in charge of sending out your email messages. So an SMTP error code basically means that your email did not get to the recipient. Keep in mind, not all SMTP codes are error codes. However, the “sent codes” are rarely ever seen, and the codes that you receive in your bounce back message generally indicate an error.

SMTP codes usually consist of three digits that carry different meanings. The digits specify what has gone wrong, in other words each digit gives some form of diagnosis to the email sending failure that happened.

The first digit indicates if the command was established and processed. However, there are five different values for the first digit, which includes (1) Command accepted by mail server but confirmation message is required, (2) Task was completed without errors, (3) Mail server accepted the request but requires more information, (4) Temporary failure encountered by mail server and you have to try again, and (5) Fatal error encountered, Mail server cannot process request. You will most likely encounter error digits (4) and (5).

Meanwhile, the second digit can mean syntax errors, status of connection, mail server status or information reply. The third digit of the SMTP error code contains the details of the status of the mail transfer.

Common SMTP Codes

Let’s take a look at the most helpful SMTP codes that indicate the status of your messages:

211 – System status message or system help reply

220 – The SMTP Service is ready

250 – Requested action accepted and completed

251 – The user is not local to the server but will forward the message anyway

252 – Recipient not verified but mail server attempts delivery

354 – Indicates mail server is ready to take message or start mail input and end with a dot

However, the SMTP codes that you really want to pay attention to are the error codes, and here are the most common:

421 – Service not available, closing transmission channel and service to shut down

450 – Mailbox busy or unavailable, thus requested mail action was not taken

451 – Server error, requested action aborted

452 – Insufficient system storage, requested action aborted

500 – Command unrecognized due to syntax error

501 – Syntax error in parameters or arguments

502 – Command not implemented

503 – Mail server encountered bad sequence of commands

504 – Command parameter not implemented

550 – Mailbox unavailable, requested action aborted

551 -  User not local to server

552 -  Storage allocation exceeded, requested mail action aborted

553 – Mailbox name invalid, requested action aborted

554 – Transaction failed

While these error codes are the most common, the ones you’ll encounter the most often are those with the 55-digit range, the most common of which is the 550 SMTP error code. The 550 code is usually generated when you’ve sent your message to an improper email address, and simply double checking the email address and resending the message will fix the problem.

If you’re doing any type of email marketing, SMTP error codes are not something to take lightly. If you consistently send messages that are getting bounce back, the receiving internet service provider – in other words, where your email is getting sent – could decide to blacklist your own email address or IP address. This could prevent all of your future email messages to that ISP, even those sent to other addresses, from getting delivered.

SMTP error codes can give you excellent insight into the technicalities of your email marketing program. Unfortunately, most marketers ignore them. By paying attention to your bounce back messages, you can usually catch mistakes and fix them, before you end up on an email blacklist.

The above image is from Dave Malkoff. Thanks Dave!

You might also be interested in:

• Why Do-Not-Reply@DomainName.com Is a Terrible Idea
• Boost Email Deliverability With a Static IP Address
• How To Deal With Bounced Email
• Use Larger Fonts for Better Delivery
• Easy Email Tests to Get You Started

Tags: bounce message, Email Marketing, smtp error, smtp error code

This entry was posted on Friday, September 10th, 2010 at 9:31 am and is filed under Email Marketing. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.