Das tritt beim managed Server und Reseller-Server auf. Oftmals bei outlook oder gmx Adressen:
: host mx01.emig.gmx.net[212.227.17.5] refused to talk to
me: 554-gmx.net (mxgmx109) Nemesis ESMTP Service not available 554-No SMTP
service 554-Bad DNS PTR resource record. 554 For explanation visit
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host eur.olc.protection.outlook.com[104.47.17.97]
said: 550 5.7.1 Unfortunately, messages from [45.9.63.145] 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.
[DB8EUR05FT047.eop-eur05.prod.protection.outlook.com
2023-07-27T20:44:35.851Z 08DB8D44BD70ED81] (in reply to MAIL FROM command)