Exchange 2010 Hybrid - On-Premise mailboxes don't receive external domain emails

Question

Hi all,&nbsp;I am going into a really weird issue, I have a Exchange 2010 Hybrid scenario, the MX records are pointed to Exchange Online.&nbsp;The issue is that On-premise mailboxes are not receiving email from external domains and the sender doesn't receive any error reply. Mail flow between Office 365 and on-premise is working fine and external domain emails are correctly delivered to Online mailboxes.&nbsp;Does someone have an idea ?&nbsp;Many thanks for your help&nbsp;&nbsp;&nbsp;

rob ellis · Answer

This is a good resource for these kinds of issues - https://blogs.perficient.com/2015/02/10/office-365-common-exchange-online-hybrid-mail-flow-issues/

vasilmichev · Answer

What does a message trace show?

amris_b · Answer

Hi Vasil,&nbsp;I have found out that the message were pending within Exchange Online because an insufficient ressource on the On-Premise server. (System was under 5Go space free, after getting some space the messages have been correctly delivered).&nbsp;Many thanks for your help

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Exchange 2010 Hybrid - On-Premise mailboxes don't receive external domain emails

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