When a message fails to be delivered to the intended recipient(s) Sedna will generate a Non-Delivery Report (NDR), which will be received to the address the message was originally sent from. The NDR will contain the recipient's email address that the message failed to send to, along with an error message generated by the recipient's mail server (see example NDR below).
Should you receive an NDR and are unsure about how to rectify this, review the below Common Reasons for Non-Delivery of messages and where relevant, reach out to our Support team via our portal.
Example NDR:
Common Reasons for Non-Delivery of Messages
Message delivery failed due to Spam
Some common errors you may see in an NDR when a message has failed to deliver to a recipient due to being marked as spam can be found below:
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553 Blocked Using Spam Pattern, Your Message May Contain The Spam Contents
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We've identified the following error: 553 Sender Domain Resolve Fail
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554 Email rejected due to security policies
If you encounter any of these error messages, it is likely that their mail server is blocking the message as spam or your domain is not noted as a whitelisted sender.
Suggested next steps:
In this case, we advise you to reach out to the recipient's IT and ask them to whitelist your sending domain and sending IP address.
If you are unsure what your sending domain or sending IP is we would recommend reaching out to support@sedna.com
Message failed due to an issue with the recipient's mail server
Some common errors you may see when a message has failed to be delivered due to issues with the recipient's mail server can be found below:
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unable to get mx info: failed to get IPs from PTR record: lookup : unrecognized address
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452 4.1.0 ... sender rejected (too busy for now)
if you encounter any of these error messages it is likely that there may be an issue with the recipient's mail server, such as server downtime or the recipient mail server is too busy to process your message.
Suggested next steps:
In this case, we would advise reaching out to the recipient's IT team so that they can look into why these errors are being returned by their server.
Message failed due to a misconfiguration with the recipient's mail server
A common error you may see when a message has failed to be delivered due to a misconfiguration with the recipient mail server can be found below:
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550 5.7.520 Access denied, Your organization does not allow external forwarding. Please contact your administrator for further assistance. AS(7555)
If you encounter this error message it is likely that the recipient's mail server is not configured to allow external forwarding.
Suggested next steps:
In this case, we would advise having the recipient contact their O365 admin to configure their mail server settings to allow external forwarding.
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