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Barracuda 550 No such user: recipient not verified

550 No such userBarracuda recipient verification failurePermanent: retrying will not helpFrom Barracuda

Example
550 No such user (user@example.com)

What it means

Barracuda gateways can check each recipient before accepting mail, either against an LDAP directory, against a list of valid users the admin maintains, or by asking the internal mail server. When that check fails, it answers RCPT TO with this 550 and the address in brackets.

For a sender, it means the address does not exist as far as the recipient organization’s gateway is concerned. Usually that is accurate. Sometimes, though, the gateway’s view is out of date or misconfigured: a new mailbox missing from LDAP, a broken LDAP bind, or an alias the verification method cannot see.

The message is refused before the body is sent and will not be retried. Compare it with “550 permanent failure ... :blocked”, where the address is valid but a filter blocked the message.

Likely causes

  • A typo in the address, or a person who has left the organization.
  • A new mailbox or alias that the Barracuda LDAP lookup or valid user list does not include yet.
  • A broken LDAP connection between the gateway and the directory, which may cause valid users to fail.
  • A shared mailbox or public folder address that the verification method does not know about.

How to fix it

  1. As the sender, double check the address and confirm it with the person another way.
  2. As the recipient admin, test the address in the Barracuda recipient verification or LDAP settings page.
  3. Fix the LDAP bind account or filter if lookups fail, and add missing aliases or shared mailboxes.
  4. Ask the sender to resend once the address verifies; the original attempt will not retry.

Checks that apply

  • MX Lookup Confirms the recipient domain’s mail flows through a Barracuda gateway or cloud service.
  • SMTP Diagnostics Connects to that MX, showing its banner and TLS setup, which helps when you report the issue to the recipient admin.
See the example diagnosed

The classification runs without network lookups and we never store your paste.

FAQ

Could the person still exist?
Yes. If their mailbox is new or the gateway’s LDAP link is broken, Barracuda may refuse a valid address. Ask them to check with their IT team.
Should I remove the address from my list?
If you cannot confirm it another way, yes. Repeated sends to unknown users hurt your reputation with that organization.

Barracuda removal request

All 191 bounce codes