550 5.7.1: sending IP blocked by Proofpoint Dynamic Reputation
Proofpoint’s IP reputation system has your sending IP on its block list because it has seen spam or viruses from it, so Proofpoint customers refuse your mail.
- Proofpoint
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 550 5.7.1
- Provider
- Proofpoint
- 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 sender. The fix is on the sending side: your domain, your server or your list.
- What the server says
550 5.7.1 Email rejected because 1.2.3.4 is listed by Proofpoint.com
What it means
Companies protected by Proofpoint Email Security check each connecting IP against Proofpoint Dynamic Reputation (PDR). Proofpoint says it delays or blocks an IP only because it is receiving spam or virus-scoring messages from it, not because of a domain or bulk mail as such. An IP that briefly shows spam is delayed for a few minutes; one that keeps sending spam is blocked and stays blocked until the spam stops for a while. This reply is the permanent form, and because the list is Proofpoint’s, it can affect mail to any company that uses Proofpoint, not just one recipient.
Common causes
- Spam, or mail that scores as spam, has been reaching Proofpoint from your IP.
- A compromised computer or account on your network sent spam through the same IP.
- You share an IP, such as a public access point or a shared mail service, with senders of spam.
How to fix it
- 01Take the IP from the bounce and check it with Proofpoint’s IP lookup.
- 02Find and stop the spam source: an infected machine, a compromised mailbox or a sending list that generates complaints.
- 03Submit a delist request from the lookup with the recipient, the type of mail and anything you fixed; Proofpoint aims to review within one business day.
- 04Ask your ISP to set your server’s reverse DNS to its mail host name if it does not already.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- PDR IP Lookup Frequently Asked Questions (Proofpoint)proofpoint.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.
- 5.7.1Delivery not authorised.The receiving server refuses the message because this sender is not allowed to send to this recipient, as a result of filtering by host or by recipient.
- 554Blocked by Proofpoint for spam or malicious activity.Proofpoint has blocked your sending IP or domain because of spam it received or malicious activity it detected, and the reply links to its postmaster page.
- 421Throttled by Proofpoint for unusual sending.Proofpoint is slowing down mail from your IP because its sending pattern looks unusual or unexpected. Your server should retry, and the delay often clears on its own.
5.7.1 at other providers
- 550 5.7.1Blocked by a domain policy.A rule set by the recipient's or the sender's Google Workspace admin blocks this message, so Gmail rejected it under that policy.
- 550 5.7.1Relay IP does not match the sending domain.Google's SMTP relay knows your IP, but the mail's sending domain is not one that IP is registered to relay for in your Workspace account.
- 550 5.7.1Blocked as likely spam.Gmail's filters judged this message likely to be spam and rejected it outright, instead of delivering it to the spam folder.
- 550 5.7.1IPv6 sender without PTR or authentication.Gmail rejected mail that arrived over IPv6 because the sending address lacks a matching PTR record, or the message failed authentication.
- 550 5.7.1Blocked for low IP reputation.Gmail permanently rejected the message because the IP it came from has a very low reputation with Gmail.
- 550 5.7.1Blocked for low domain reputation.Gmail permanently rejected the message because the domain it comes from has a very low reputation with Gmail.
Further reading
All 3 Proofpoint codesEvery code in the wikiPaste your own bounce