550: sender address blocked by the recipient
The recipient’s Barracuda gateway refuses your sender address or domain, usually because the company has blocked it.
- 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 email address rejected.
What it means
Barracuda lists this reply, and the shorter Sender Rejected, for messages refused because of the sender address. On a Barracuda gateway that usually means the address or its domain is on the company’s sender block list, set by its administrators. The rejection is permanent for that message and will repeat until the entry changes. Your server, IP and reputation are not the issue, so nothing on your side will fix it short of using a different address, which is only appropriate if the block was a mistake you cannot get corrected.
Common causes
- The company blocked your address or your whole domain.
- A block on your sending platform’s envelope domain caught your mail along with others.
How to fix it
- 01If the contact is wanted, ask the recipient through another channel to have their IT team remove the block.
- 02If your platform’s shared envelope domain is the blocked one, set up a custom return-path domain of your own.
- 03Resend once the block is lifted.
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.
- 550Sending 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.
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.
All 11 Barracuda codesEvery code in the wikiPaste your own bounce