Outlook is an email provider for predominantly Outlook, Hotmail, and Live freemail addresses, headquartered in Washington as part of Microsoft. For legitimate messages going to the spam filter or getting blocked, you'll likely need to file a false-positive report with Outlook support. For globally-blocked IPs, the adminstrator of the IP will need to request delisting directly.
smtp;451 4.4.0 Message failed to be replicated: No healthy secondary server available to accept replica at this time. [outlook.com]
smtp;451 4.7.0 Temporary server error. Please try again later. PRX6 NextHop: outlook.com [outlook.com]
smtp;550 5.5.0 Requested action not taken: mailbox unavailable. [#.eop-nam12.prod.protection.outlook.com]
smtp;550 5.7.1 Service unavailable, MailFrom domain is listed in Spamhaus. To request removal from this list see https://www.spamhaus.org/query/lookup/ (S8002) [#.eop-nam02.prod.protection.outlook.com]
smtp;550 5.7.1 Unfortunately, messages from [x.xx.xx.xx] 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. [#.eop-nam02.prod.protection.outlook.com]