Spam filter / gateway
Barracuda SMTP Error Codes and Rejection Messages
Barracuda is a mail security gateway for businesses. Mail routes through Barracuda before the recipient's server, and while recipients manage their own allowlists, a reputation issue affecting all Barracuda customers has to go through Barracuda support.
- Codes on record
- 6
- Responses
- 14
Postmaster & documentation
SMTP 4212 responses
A temporary problem. The sending server keeps retrying for a while, and delivery often recovers on its own once the underlying issue clears. See SMTP 421 across every provider
SMTP 4221 response
A temporary problem. The sending server keeps retrying for a while, and delivery often recovers on its own once the underlying issue clears. See SMTP 422 across every provider
SMTP 4501 response
A temporary problem. The sending server keeps retrying for a while, and delivery often recovers on its own once the underlying issue clears. See SMTP 450 across every provider
SMTP 4513 responses
A temporary problem. The sending server keeps retrying for a while, and delivery often recovers on its own once the underlying issue clears. See SMTP 451 across every provider
SMTP 5505 responses
smtp;550 cuda_nsu 5.1.1 <[email protected]>... User unknown
smtp;550 No such user ([email protected])
smtp;550 Blocked
smtp;550 rejecting spoofed message
A hard failure. The receiving server has refused the message for good and will not accept an unchanged retry without a change on the sending side. See SMTP 550 across every provider
SMTP 5542 responses
A hard failure. The receiving server has refused the message for good and will not accept an unchanged retry without a change on the sending side. See SMTP 554 across every provider
Barracuda bounce questions
›Why is Barracuda bouncing my email?
Barracuda is a mail security gateway for businesses. Mail routes through Barracuda before the recipient's server, and while recipients manage their own allowlists, a reputation issue affecting all Barracuda customers has to go through Barracuda support. Match the exact wording of your bounce to one of the 14 responses on this page to find the specific reason and fix.
›How do I get past the Barracuda spam filter?
Authenticate with SPF, DKIM and DMARC, keep your sending IP and domain reputation clean, mail only engaged recipients, and honour unsubscribes. Barracuda also publishes postmaster guidance, linked on this page.
