This is the mail system at host mailout03.t-online.de.

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<xxxx@hotmail.com>: host hotmail-com.olc.protection.outlook.com[104.47.2.33]
said: 550 5.7.1 Unfortunately, messages from [194.25.134.81] weren't sent.
Please contact your Internet service provider since part of their network
is on our block list (S3140). You can also refer your provider to
http://mail.live.com/mail/troubleshooting.aspx#errors.
[DB5EUR01FT014.eop-EUR01.prod.protection.outlook.com] (in reply to MAIL
FROM command)

<xxxxcxx@live.be>: host eur.olc.protection.outlook.com[104.47.13.33] said: 550
5.7.1 Unfortunately, messages from [194.25.134.81] weren't sent. Please
contact your Internet service provider since part of their network is on
our block list (S3140). You can also refer your provider to
http://mail.live.com/mail/troubleshooting.aspx#errors.
[HE1EUR04FT017.eop-eur04.prod.protection.outlook.com] (in reply to MAIL
FROM commaxxx@hmail.com>: host hmail.com[69.65.10.209] said: 550 No Such User Here
(in reply to RCPT TO command)