550: sending IP blocked by the recipient
The recipient company’s Barracuda gateway refuses mail from your sending IP, usually because an administrator has added it to a block list on their side.
- Barracuda
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 550
- Temporary or permanent
- PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
- Who has to act
- The recipient's side. Their mail admin has to change something; you can tell them.
- What the server says
550 Sender IP address rejected.
What it means
Barracuda lists this reply, and the shorter Blocked IP address, for a connecting IP the gateway has been told to reject. That is typically an entry in the gateway’s own IP block list, set by the recipient company’s administrators, rather than a public blocklist. The rejection is permanent and will repeat for every message from that IP to this company until the entry is removed. Other companies are not affected, which helps tell it apart from a reputation problem: if mail from the same IP reaches other Barracuda customers, the block is local.
Common causes
- An administrator at the recipient company blocked your IP or its range.
- Your IP is shared with a sender the company blocked.
- An old block from an earlier incident was never removed.
How to fix it
- 01Check whether mail from the same IP reaches other companies; if it does, the block is local to this one.
- 02Contact the recipient through another channel and ask their IT team to remove the IP from their Barracuda block list.
- 03If the IP is shared and stays blocked, send from a different IP or provider.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- SMTP Error Codes, Barracuda Email Security Gateway documentationdocumentation.campus.barracuda.com
Related codes
- 550Mailbox unavailable.The receiving server permanently refused the message for this recipient: the mailbox does not exist, cannot be reached, or the server rejected the message by policy.
- 550Sender address blocked by the recipient.The recipient’s Barracuda gateway refuses your sender address or domain, usually because the company has blocked it.
550 at other providers
- 550 [SC-001]Outlook.com policy block for content or reputation.Outlook.com rejected the mail for policy reasons tied to spam-like content or to the reputation of the sending IP or domain.
- 550 [SC-002]Outlook.com block for namespace mining.Outlook.com blocked the sending IP because it behaved like a namespace miner, checking whether addresses exist without sending mail.
- 550 [SC-003]Outlook.com block for an open proxy or relay.Outlook.com rejected the mail because the sending IP appears to be an open proxy or open relay.
- 550 [SC-004]Outlook.com block after complaints.Outlook.com placed a block on the sending IP because it received complaints about mail coming from it.
- 550 [DY-001]Outlook.com refuses dynamic IP addresses.Outlook.com rejected the mail because the sending IP is dynamic address space, which it generally does not accept mail from.
- 550 [DY-002]Outlook.com block for a likely compromised sender.Outlook.com rejected the mail because the sending server or computer appears to be compromised or infected.
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