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
0 Non-bounce Other
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
60 Auto-reply Other
70 Transient bounce Other
90 Unsubscribe request Hard
100 Challenge response Other
110 Over eMailPlatform throttle limit Other
120 Queue dumped 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
200 Spam complaint NA

 

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.

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