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Blacklist/whitelist Outlook mails



  • cPRex Jurassic Moderator

    Hey there!  There isn't going to be anything you can do to resolve this issue on the server, as that error message indicates your server's IP address is blocked.  You'll need to contact your hosting provider or datacenter to have them work with Microsoft to resolve the issue.


    Ah the dreaded S3150. You have my sympathies.

    First off check your IP reputation in Smart Network Data Services (SNDS) at if you are not enrolled yet I highly suggest doing so including your hostingprovider it is one of the things that is checked when you request the delist.

    Next check if you have a history of IP reputation messages if not than most likely your not the problematic IP but more than likely it is either a false positive or they did a range block instead.

    Check your IP range and those of your neighbors in a service like Cisco Talos Intelligence 

    If those are showing signs of reputation issues at email delivery tell your hosting provider to take a further look at the matter as the release procedure (conditional mitigation) from Microsoft can get blocked if there are ongoing issues.

    If actions are taken by your hostingprovider or nothing strange is showing up than fill in the following SRX form and ask your hosting provider to do the same.

    9 out of 10 times it will get rejected the first time. Simply reply that you request a review and someone from will contact you on the provided mail address and either reject or tell you that the IP received conditional mitigation.

    It is better in our experience to send the request double as both server admin as well as datacenter because response to these matters can be finicky. Expect a waiting time from 72 hours to two weeks in extreme cases and after mitigation status is granted 24 to 48 hours replication time to resolve the issue.


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