Today while trying to send a email from my email server to a @hotmail account I got: (my IP suppressed in the following copy)
"outlook-com.olc.protection.outlook.com[184.108.40.206] said: 550 5.7.1 Unfortunately, messages from [*.*.*.*] 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. [SN1NAM01FT015.eop-nam01.prod.protection.outlook.com] (in reply to MAIL FROM command)"
Accordingly the guidelines "https://sendersupport.olc.protection.outlook.com/pm/troubleshooting.aspx" there are 8 different cases for '550' code, from 550 SC-001 to 550 OU-002 but the message returned to my host doesn't specify which was the case among the 8. it looks like a important piece of information to get started troubleshooting.
1- Anyway, most importantly: The message says that "... part of their network is on our block list ...". It means that outlook host is really blocking entire subnets? As example in the /24 sub my IP is located just 2 IP's have a poor email reputation, one of them is blacklisted, and it's not my IP. (Scanned with https://www.talosintelligence.com/reputation_center)
2- And finally: Have been using my IP for years now without problems, sending low-traffic e-mails for just one domain. Checked my logs and had just one email sent to outlook destinations (@hotmail.com, @live.com, etc) in the last 7 days, and it's this one that was blocked. If it's true that outlook blocks entire IP ranges there's a way to have my specific IP in a whitelist?
Appreciate any clue.