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{LED=451 4.4.397 Error communicating with target host. -> 421 4.2.1 Unable to connect -> SocketTimedout: Socket error code 10060

Niranjan T Pattana Shetty 291 Reputation points
2022-10-26T13:56:54.833+00:00

Hi All,
We have a hybrid environment in our infra and all of our mailboxes are hosted in Office365, and we have mail-flow triggered from applications happen from On-Prem Exchange, and sometimes as seen in the question title, we receive such errors, not sure what could be the issue here.

Need some guidance on the same.

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.
7,581 questions
Microsoft Exchange Hybrid Management
Microsoft Exchange Hybrid Management
Microsoft Exchange: Microsoft messaging and collaboration software.Hybrid Management: Organizing, handling, directing or controlling hybrid deployments.
2,060 questions
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  1. Andy David - MVP 147.4K Reputation points MVP
    2022-10-26T14:31:54.007+00:00

    Do you have any firewall rules that restrict outbound on port 25 from on-prem Exchange to Exchange Online?

    https://learn.microsoft.com/en-us/microsoft-365/enterprise/urls-and-ip-address-ranges?view=o365-worldwide

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  1. Niranjan T Pattana Shetty 291 Reputation points
    2022-10-27T04:12:27.517+00:00

    Hi AndyDavid,
    Thanks for the advise, the issue was the application was using the UPN to route mails and UPN wasn't added into the aliases, so the above error was generated. Thanks again.

    1 person found this answer helpful.
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