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pavankumar-6152 avatar image
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pavankumar-6152 asked LucasLiu-MSFT commented

Exchange to Office 365 - Hybrid mail flow

Hello,

I have a problem sending an emails using the Outbound to office 365 connector in on-prem exchange . it is throwing an error when i am sending a email to office 365 mailbox which is migrated.

error :

Server at domain.mail.onmicrosoft.com (52.47.64.127) returned '451 4.4.397 Error communicating with target host. -> 421 4.2.1 Unable to connect -> SocketConnectionRefused: Socket error code 10061'

Any idea, how can i resolve this.

Thank you.

office-exchange-server-administrationoffice-exchange-online-itprooffice-exchange-server-mailflowoffice-exchange-server-connectivityoffice-exchange-hybrid-itpro
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AndyDavid avatar image
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AndyDavid answered

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LucasLiu-MSFT avatar image
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LucasLiu-MSFT answered LucasLiu-MSFT commented

Hi @pavankumar-6152 ,
Can you successfully send mail to other external recipients?
All user met this issue or only sepecific user meet?
According to the research on error information:
1.Is there a firewall? If so, please make sure that there is no firewall blocking access to the O365. Check the firewall to ensure that all ports required by Exchange are opened, especially 25 and 587. And there is no policy to prevent the necessary communication. If possible, please try to temporarily shut down.

2.Please following the steps to check the DNS loopups:
Open the EAC -> Servers -> Servers -> Edit -> DNS lookups -> Make sure that already set up the DNS lookups.

3.Please make sure that the delivery, address space and source server of send connector are correct.



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hello lucas

  1. Yes i can send email to external recipients (like Gmail, Outlook or any other domain).

  2. This is for all the users from on-prem email server to office365 receipents in Hybrid centralized mail flow.

Can i also get the link for all the available url's & Ips & ports that i need to open to communicate with office365. i want to cross verify.

Thanks.



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Hi @pavankumar-6152 ,
Please refer the article link porivde by Andy.



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