IP-Sperre von Microsoft aufheben lassen

Microsoft sperrt anhand von unklaren Richtlinien scheinbar wahllos IP-Adressen für die Maileinlieferung zu ihren Diensten (outlook.com, hotmail.com, live.de,…). Traurige Beispiele dafür findest du bei Disroot und hier. Nachfolgend findest du ein paar Hinweise zum Vorgehen, um die eigene IP-Adresse entsperren zu lassen.

• Auf der Ebene des Mailservers ist die Sperrung an gescheiterten TLS-Verbindungen zu MS-Diensten zu erkennen:

  relay=hotmail-com.olc.protection.outlook.com[104.47.0.0]:25, delay=2.9, delays=2/0/0.67/0.18, dsn=5.7.1, status=bounced (host hotmail-com.olc.protection.outlook.com[104.47.0.0] said:
  550 5.7.1 Unfortunately, messages from [51.75.0.0] weren't sent. Please contact your Internet service provider since part of their net work is on our block list (S3140).
  You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. [SG2APC01FT042.eop-APC01.prod.protection.outlook.com]

• Der Umfang der Sperre lässt sich anhand des Fehler-Codes erkennen:
  • S3140: IP ist vollständig blockiert,
  • S3150: IP ist gedrosselt.
• Über den Smart Network Data Service (SNDS) kannst du den Status deiner IP-Adressen einsehen. Eine vorherige Anmeldung ist dafür notwendig.

Die folgenden Tests geben Hinweise darauf, ob mit deinem Setup alles in Ordnung ist:

• https://www.mail-tester.com/
• https://www.internet.nl/
• https://talosintelligence.com/reputation_center
• https://www.suped.com/tools/email-tester

Delisting request — IP 194.164.48.221 blocked by Outlook.com/Hotmail (S3150)

Hello,

I would like to request review/delisting of IP address 194.164.48.221 from the Outlook.com/Hotmail block
list.

Server details:
- Sending IP: 194.164.48.221
- Hostname (PTR and forward DNS match): web02.kohlweiss.domains
- Mail software: Postfix on Linux (Plesk-managed)

Rejection observed:
On 2026-10-06 at 08:46:19 UTC, a legitimate message was rejected during the MAIL FROM phase with:

550 5.7.1 Unfortunately, messages from [194.164.48.221] 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=11BE461A669B11DA] [MI3PEPF0000855E.eurprd05.prod.outlook.com 2026-10-06T08:46:19.748Z
08DF230D33EB04E7]

Checks performed and findings:

1. Reviewed the Postfix mail queue: empty, no backlog.
2. Reviewed mail logs for the affected period: normal, low outbound volume. No evidence of a compromised

mailbox, unauthorized relay use, unusual SASL authentications, or script/webform abuse.

1. Verified PTR record for 194.164.48.221 resolves to web02.kohlweiss.domains, matching the server's forward

DNS (A record) and its SMTP EHLO name.

1. Implemented and verified SPF, DKIM (2048-bit RSA), and DMARC for the affected sender domain

(virgolini.com).

1. Confirmed via independent third-party test (mail-tester.com, score 7.9/10) that SPF, DKIM, and DMARC all

pass, and that this IP is not listed on any of 20 common public blocklists, including Spamhaus SBL, XBL,

  PBL, and CSS.

Given the very low and normal sending volume, the absence of any abuse indicators, fully compliant
authentication, and a clean reputation across all checked blocklists, we believe this IP (or a shared range
it belongs to) was listed as a result of activity from other senders on the same network, rather than from
this server. We would appreciate confirmation of what is required for delisting, and whether this is an
IP-specific listing or a range-level one.

The complete SMTP rejection / NDR is attached below for reference.

Thank you for your assistance.

Regards,
Thomas Kohlweiss