Email bounces and explanation of bounce codes
When you send an email to a contact from eMailPlatform, a response will be sent back from the recipient’s mail server to eMailPlatform’s mail server. If the email bounces, there are a number of different codes that indicate why it happened that can be gathered from the recipient’s mail server. From time to time, it may however be problematic to accurately diagnose exactly why an email bounces, as not all mail servers are equally good at returning a precise answer to why an email bounces.
3 types of email bounce codes
There are 3 different types of email bounce codes: Hard, Soft, and Other. These can be explained as follows:
Hard bounce: A hard bounce occurs when the incoming mail server at the recipient announces that the email address is not valid. Typically, this will mean that the user does not exist.
Soft bounce: A soft bounce is a condition where the email address of repeating soft bounces must be declared invalid. An example of this is a code 21 (see below). This can occur if the domain name no longer exists, or the DNS registration has expired or will be renewed tomorrow or there was a temporary error in DNS lookup. If code 21 is continuous, the email address can be declared invalid.
Other: This is a state where reception fails, but where it is not the email address that poses a problem. The problem here can be spam blocking. Instead of completely removing the email address, you should instead investigate and resolve the spam issue so that you can resend to the email address.
|Code||Description||Type||Example of SMTP response|
|10||Bad email address||Hard||550 User Unknown|
|20||Temp failure – General||Soft|
|21||Temp failure – DNS Failure||Soft|
|22||Temp failure – Mailbox full||Soft|
|23||Temp failure – Message size too large||Other|
|29||Temp failure – Unable to connect||Soft|
|30||Bounce with no email address||Other|
|40||General bounce||Other||Sorry, I wasn’t able to establish an SMTP connection. (#4.4.1)/I’m not going to try again; this message has been in the queue too long|
|50||Mail block – General||Other|
|51||Mail block – Known Spammer||Other|
|52||Mail block – Spam detected||Other|
|53||Mail block – Attachment detected||Other|
|54||Mail block – Relay denied||Other|
|59||Mail block – Unable to connect||Other|
|110||Over eMailPlatform throttle limit||Other|
|121||Delivery paused then message expired||Other|
|122||Suppressed by System due to Subscriber Inactivity||Other|
|123||Blocked due to System policy enforcement||Other|
Below are the individual bounce error codes. See the description of the individual error codes below the table.
0 – Non-bounce
Occurs when the incoming mail server’s bounce processor receives an email that it indicates for not having to bounce.
29 – Soft bounce – Unable to connect
This is a soft bounce where it was not possible to connect to the incoming server. If there are many bounces with this code for a single domain, then it typically means either that the domain is not working or that the domain has blocked the eMailPlatform mail server.
59 – Mail block – Unable to connect
This is a bounce type closest to the above bounce code 29. However, this is a large domain, with some assurance that the domain may still exist. Therefore, the reason for bounce is likely to block all connections from your IP address. Some of the larger domains will completely block your IP address when you try to connect to their mail servers in a blacklisting process.
110 – Exceeded eMailPlatform’s throttle limit
This bounce type occurs when an email that has been in the queue over the specified queue-limit time has been scheduled for delivery, but delivery can not be completed. This because it will exceed the set limit for the amount of emails that can be received on the recipient’s incoming mail server within a given time period.
120 – Queue dumped
With this type of bounce, eMailPlatform has been prompted to dump all messages in the queue.
121 – Delivery paused then message expired
With this type of bounce, eMailPlatform has been prompted to pause all messages in the queue. After the maximum number of attempts has been reached, these emails bounce with this code.
122 – Suppressed by System due to Subscriber Inactivity
By this bounce, eMailPlatform has chosen not to send to the recipient because it has not responded to, for example, clicking on a link or loading images, both indicating engagement from the recipient’s page. That is, it is an inactive recipient.
123 – Blocked due to System policy enforcement
At this bounce, eMailPlatform has chosen not to send to the recipient due to policy issues.