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HishamAbdallah-3005 avatar image
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HishamAbdallah-3005 asked KyleXu-MSFT commented

emails do not reach some domains

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

office-exchange-server-mailflowoffice-exchange-server-connectivity
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That IP is on a blocklist.

Are you sending from on-prem to Office 365? Or 365 to another domain?

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KyleXu-MSFT answered

@HishamAbdallah-3005

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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