Automatic reply not working to external recipient

Question

Automatic reply not working to external recipient

Geezer32 111

I have some shared mailbox with OOO setup to message externals, and this isn't working. I also tested on my own Outlook setting an OOO with externals enabled and this isn't working either. ooo is received by internals but not to externals.

The Defender anti-spam Outbound policy for external forwarding is set to "system Managed" which=block as far as I know, but is this setting affecting auto-replies also? I thought that auto-reply/ooo was not the same thing as auto-forward.

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Answer 1

Raymond-K 160 Microsoft External Staff Moderator

Hi Geezer32,

Thank you for posting your question in the Microsoft Q&A forum.

There are some configurations could affect external OOF. Please use the following command to check if remote domain blocks OOF replies:

Get-RemoteDomain | ft -AutoSize Name, DomainName, AutoReplyEnabled, AllowedOOFType

Please confirm that AutoReplyEnabled is set to True. For your reference:

Remote domain blocks OOF replies

Also, you can create a message trace, and check if the external OOF message is blocked with any error description during email processing:

EAC > Mail flow > Message trace > Start a trace

Message trace in the new EAC in Exchange Online | Microsoft Learn

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Geezer32 111 Reputation points

2025-04-29T00:37:48.5433333+00:00

Thanks for the info

We are a hybrid Exchange org, the remote domain config is "External" for OOF

The MS article does not do a good job of explaining clearly the difference between 'External' and 'ExternalLegacy' but it seems like 'External' should be correct to allow external OOF to be routed to Exchange hybrid?

This is working with on-prem mailboxes but not for any online mailbox

Message trace isn't telling me anything because no message is being generated at all.

I am unclear which thing is affecting this, as mentioned, the default Defender Anti-Spam policy for outbound is blocking auto-forward. This should be different from OOF auto reply, but I have read many messages saying that this also affects the OOF response.
Hien-L 4,340 Reputation points Microsoft External Staff Moderator

2025-04-30T07:24:41.97+00:00
Hi @Geezer32 ,

In general, it needs to wait for some time to generate message trace logs after delivering one email. It’s strange that we cannot see any internal or external OOF message from message trace. Also, the OOF only send once for the same recipient.

Here are additional suggestions for you:

Since the OOF is generated by O365 mailbox and is not forwarding email, the configuration for email forwarding in outbound spam filter policy will not affect OOF emails.

Please turn off the OOF and turn it on again, then send test email to this mailbox from internal and external senders. Make sure that the O365 mailbox could receive test emails, and your internal sender could receive internal OOF at least.

Wait for 10-20 minutes. Create a message trace, specify the sender address (mailbox that turn on OOF) and the time range. Please check if any log entries for internal and external automatic replies.

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".

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Automatic reply not working to external recipient

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