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What is the cuda_nsu SMTP response and why am I seeing it?

  • Type: Knowledgebase
  • Date changed: 3 years ago
Solution #00006048

This applies to all Barracuda Spam and Email Security Gateway.

The Barracuda Spam and Virus Firewall performs recipient verification via several methods. This process occurs during the time envelope details on a new email message are received.

One of these methods is via SMTP Verification. When an email comes in destined for a user, the Barracuda will contact its configured domain destination server, and perform a 'mail from / rcpt to' test, and then literally proxy the response it got back from the SMTP server on trying to deliver to that user.  This information is then relayed to the sending connection as cuda_nsu: < the response >

Maintaining an active list of cuda_nsu responses and their responsive server types:

If you are seeing the reason "Forwarding to remote hosts disabled" This is because they have a setting on the mail server to exempt domains in exception rules. 

(cuda_nsu No such user (so'hare) -ERR Single quotes not permitted in usernames )

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