Hello,
Can you please share the complete bounce email? It contains important diagnostic data that helps shed some light of the root cause. Feel free to redact personal information when you share.
My emails are not being sent to 3 separate email addresses (S3150)
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Wendy White
20
Reputation points
My emails are not getting through to 3 email addresses. I have not had problems with 2 of them at all until now. I am receiving a S3150 message. I don't know why this is happening as I do not bulk spam people and I only send out emails occasionally. I have tried finding out what to do on the Microsoft website but it is very confusing to me. How can resolve this issue please?
Outlook | Windows | Classic Outlook for Windows | For home
Answer accepted by question author
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EmilyS726 213K Reputation points Independent Advisor2026-02-14T04:08:29.33+00:00 -
Wendy White 20 Reputation points
2026-02-14T04:13:05.0833333+00:00 This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed:
host hotmail-com.olc.protection.outlook.com [52.101.40.7]
SMTP error from remote mail server after pipelined sending data block:
550 5.7.1 Unfortunately, messages from [103.150.252.185] 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.atruncated]
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EmilyS726 213K Reputation points Independent Advisor
2026-02-14T04:41:17.1733333+00:00 This is the key detail: 103.150.252.185 is the sending server’s public IP address that tried to deliver the email to Microsoft. Microsoft blocked that IP, so delivery failed.
This means, the IP is in a range that has high spam activities. Who's your email service provider?
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Wendy White 20 Reputation points
2026-02-14T04:55:26.12+00:00 Optus. I've already contacted Optus and they can't find any problems on their end.
I only spoke to one person so that doesn't necessarily mean that there isn't a problem with Optus as the service provider.
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EmilyS726 213K Reputation points Independent Advisor
2026-02-14T05:16:05.43+00:00 I’m not sure your provider would automatically know an IP is being used for spam. This is usually detected on the receiving side, or by third party anti spam services that monitor sender reputation. In this case, Microsoft rejected the message because the sending IP 103.150.252.185 is on their block list (S3150). That IP is the public IP of the outbound email server or relay used to send the message, not the sender’s home internet IP. Inform Optus. Sender’s email service provider does a mix of investigation, cleanup, and reputation repair. Unfortunately this is out of your control now.
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Wendy White 20 Reputation points
2026-02-14T05:42:28.5766667+00:00 So, if I contact Optus again and let them know what you just stated; will they be able to resolve the problem? And, is this something Optus has to fix on their end?
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EmilyS726 213K Reputation points Independent Advisor
2026-02-14T06:12:19.38+00:00 Yes they will have to fix this. I certainly hope they know what to do.
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Wendy White 20 Reputation points
2026-02-14T04:12:40.9566667+00:00 This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed:
host hotmail-com.olc.protection.outlook.com [52.101.40.7]
SMTP error from remote mail server after pipelined sending data block:
550 5.7.1 Unfortunately, messages from [103.150.252.185] 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.atruncated]