Error types and codes
This article explains the difference between soft and hardbounces and how to handle errors.
E-mail error codes
When an email can not be delivered the receiving mailserver usually sends an error code back in a message with a short description of the error. There are two main types:
- Soft bounces: temporary errors. Error codes start with a 4 (4.XX)
- Hard bounces: persistent errors. Error codes start with a 5 (5.XX)
Identifying an error
The difference between hard an softbounces seems simple, but in actuality there are many possible causes for an email not reaching its destination, whether temporarily or permanently. Since knowing the difference between hard and softbounce is not sufficient to remedy every problem we prefer looking at where the mistake occurred in the process of sending the email.
Processing an email and delivering it is done in five steps.
- Step 1: The domain name is converted to an IP-address
- Step 2: A connection is established with the IP-address
- Step 3: Connection is made with the receiving mailserver, Hotmail for example.
- Step 4: The email is accepted by the receiving mailserver or sends an error code back.
- Step 5: If the email fails later, even when accepted by the server, the email is sent back to us, usually with an error code. You can read more information about these error codes here.
Sometimes an error between step 1 through 3 is classified as a hard bounce and everything after as a soft bounce. Other times 1 through 4 is classified as a hardbounce. Other times the steps are ignored and the error code is used to determine whether a soft- or a hardbounce occurred.
You can find the errors occurring from your mailings in the Error tab. The error code is also specified here if it exists. You can also have them delivered to a script on your own server with WebHooks.
Solving errors
How to solve an error depends on the user of the software and the receiver. Some users might have another route to contact the receiver, such as calling, to get the correct email address if this is the problem.
If emails are never delivered to certain addresses it is better to remove them from the database or not email them. It is possible to make a selection based on errors by using selection type "Check on email results" and selecting result "No error must have been registered".