topic Re: URGENT: SMTP Relays Blocked by Microsoft (Errors S3150 and S3140) in Email

URGENT: SMTP Relays Blocked by Microsoft (Errors S3150 and S3140)

1Char1695 — Sat, 28 Feb 2026 14:57:39 GMT

Hi Team,

I am unable to send emails to Microsoft domains (Hotmail/Outlook) via the Apple Mail app. The phone support team suggested this was a device issue, but the bounce-back reports clearly show a Plusnet server reputation fault.

The specific error details from my logs are:

Relay 1: 84.93.230.235 (Error S3150)
Relay 2: 212.159.14.17 (Error S3140)

Full Diagnostic Code: Diagnostic-Code: smtp; 550 5.7.1 Unfortunately, messages from [212.159.14.17] weren't sent. Please contact your Internet service provider since part of their network is on our block list (S3140).

This confirms the issue is with the Plusnet SMTP network reputation. Could the NetOps team please investigate these IPs and request a delisting from Microsoft?

My settings are verified as Port 587 with Password Authentication.

Re: URGENT: SMTP Relays Blocked by Microsoft (Errors S3150 and S3140)

1Char1695 — Sat, 28 Feb 2026 15:01:35 GMT

Update: The email sends perfectly when I turn off Wi-Fi (I have plusnet wifi) and use Mobile Data. This confirms my device settings are correct and the issue is strictly with the Plusnet Broadband SMTP relay reputation.

Re: URGENT: SMTP Relays Blocked by Microsoft (Errors S3150 and S3140)

PhilipHeyes — Sat, 28 Feb 2026 15:13:50 GMT

Take a read at :

https://community.plus.net/t5/Email/Hotmail-rejecting-mail-from-PN-Diagnostic-Code-smtp-550-5-7-1/td-p/2035800

Re: URGENT: SMTP Relays Blocked by Microsoft (Errors S3150 and S3140)

Baldrick1 — Sat, 28 Feb 2026 15:20:29 GMT

Moderator's note:
Duplicate post released from the automatic spam filter and removed.