emails do not reach some domains

Hisham Abdallah 6 Reputation points
2021-10-05T09:31:36.097+00:00

I get the following error in the mail queue

LED=451 4.4.0 Primary target IP address responded with: "421 service not available (connection to blacklisted host (104.47.6.36 - DNSBL))." Attempted failover to alternate host, but that did not succeed.

can someone explain what does this mean?
thank you

Exchange Server Management
Exchange Server Management
Exchange Server: A family of Microsoft client/server messaging and collaboration software.Management: The act or process of organizing, handling, directing or controlling something.
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  1. KyleXu-MSFT 26,206 Reputation points
    2021-10-06T02:21:55.067+00:00

    @Hisham Abdallah

    emails do not reach some domains
    connection to blacklisted host (104.47.6.36 - DNSBL)).

    Which mail server that you send emails from?

    Since you could send emails to some other mail server. I think you need to confirm with the mail server side which you cannot send email to. Whether they configure any filter services block your mail server.

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