RBL from microsoft (hotmail) should generate an insight
An example of log line is:
Feb 18 11:55:37 mail postfix/smtp[19793]: 6BAB0300C9CD: to=<someone@hotmail.com>, relay=hotmail-com.olc.protection.outlook.com[104.47.66.33]:25, delay=0.7, delays=0.04/0.02/0.47/0.16, dsn=5.7.1, status=bounced (host hotmail-com.olc.protection.outlook.com[104.47.66.33] said: 550 5.7.1 Unfortunately, messages from [1.2.3.4] 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. [MW2NAM12FT005.eop-nam12.prod.protection.outlook.com] (in reply to MAIL FROM command))