Failed Recipient: <Mod remove PII> @hotmail.com

Question

Failed Recipient: <Mod remove PII> @hotmail.com

Reason: Remote host said: 550 5.7.1 Unfortunately, messages from [203.150.224.21] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3150). You can also refer your provider to [http://mail.live.com/mail/troubleshooting.aspx#errors]. [Name=Protocol Filter Agent][AGT=PFA][MxId=11BC9CB6E38576AC] [AM3PEPF0000A796.eurprd04.prod.outlook.com 2026-01-09T10:12:56.816Z 08DE4E5B738E7364]

Please help to resolve it

Answer 1

The error message you received indicates that your email was blocked by the recipient's email server due to your sending IP address being on a block list. Specifically, the error code 550 5.7.1 suggests that messages from your IP address (203.150.224.21) are not being accepted by the recipient's server, which is likely due to a security policy or blocklist entry.

To resolve this issue, you can take the following steps:

1. Contact Your Internet Service Provider (ISP): Inform them that your IP address is on a block list and request assistance in getting it removed.
2. Check Your IP Reputation: You can use various online tools to check if your IP address is listed on any blocklists and follow the necessary steps to delist it if applicable.
3. Follow Best Practices: Ensure that your email sending practices comply with best practices for email deliverability to avoid being flagged as spam in the future.

For more detailed guidance on resolving non-delivery reports, you can refer to the relevant documentation provided by Microsoft.

---

References:

• Email non-delivery reports and SMTP errors in Exchange Online