Rule to filter out emails sent to EOL outbound connector (Centralized Transport mode enabled)

Question

Rule to filter out emails sent to EOL outbound connector (Centralized Transport mode enabled)

Evi Venizelou 1

Our tenant [domain contoso-x.com] hosts several subsidiaries' domains [other-y.com, another-z.com].
Only for our main domain [contoso-x.com] we will implement Hybrid with option Centralized Transport mode enabled.
Our target is to forward any email sent from contoso-x.com mailbox on the cloud to our OnPrem environment (via an EOL Outbound Connector] and relay it to the internet in a Secure Email Gateway we possess.
As Centralized Transport will send any email sent from any hosted domain in our tenant to the onprem environment, we are looking for a rule to filter-out any other email sent from subsidiaries' domains to EOL Outbound connector and keep only emails from our main domain contoso-x.com

2 answers

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Answer 1

Lucas Liu-MSFT 6,191

Hi @Evi Venizelou ,
In order to better help you, I want to confirm with you that whether all the mailboxes are in Exchange online? If so, based on my research and test, you could following the steps to make only emails from your main domain send to on-premises Exchange server.

1.Please disable the centralized tranpsort mode first. We could not create a connecotr from Office 365 to Internet. So we cannot create a transport rule to specify that users use a connector that is sent directly to the Internet. Disbale the centralized transport mode will send all emails directly to Internet.

2.Create a connector as below screenshot. Set to "From: Office 365" and "To: Your organization's email server". And select "Use only when I have a transport rule set up that redirects messages to this connector."

3.Create a transport rule as below screenshot. Set to use the specific connector you just created to send mail when the sending domain is your main domain, then the mail will be sent to your On-premises Exchange server. Initially, you can set "Apply this rule…" to a specific sender, then send a test email to external recipient and see if the email send to on-premises Exchange server first.If it succeeds, set it apply to all users in the domain, so as to prevent accidents from affecting the use of the user's mailbox.

The following is my test in lab environment:
1.I create a connector and transport rule as I mentioned above, then I send a email to external recipient. First, I check the message track in Exchange online and view the email send to my on-premises Exchange server.

2.Second, I check the message tracking log in on-premises Exchange, we could see that the email is transmitted in the on-premises Exchange server and sent out successfully.

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VenizelouE 1 Reputation point

2021-05-09T10:52:52.877+00:00

Hi @Lucas Liu-MSFT .
Thanks for the immediate answer.
To answer your question, most of our main domain's mailboxes will be kept on prem but the rest will be moved to the cloud.
BR, Evi
Lucas Liu-MSFT 6,191 Reputation points

2021-05-10T08:22:29.88+00:00

Hi @VenizelouE ,
For the user mailbox in on-premises Exchange server, no matter whether "centralized mail transport" is enabled or not, it will be sent directly from on-premises Exchange server.

For the user mailbox in Exchange online, you could following the steps I provide above. As I said above, in order to avoid unexpected situations affecting the use of all user mailboxes, you could specify only one user mailbox when creating a transport rule, and then test whether the mail flow and sending and receiving of the mailbox are normal.

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Lucas Liu-MSFT 6,191 Reputation points

2021-05-14T09:35:23.917+00:00

Hi @VenizelouE ,
I am writing here to confirm with you how thing going now?

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Lucas Liu-MSFT 6,191 Reputation points

2021-05-20T08:34:47.197+00:00

Hi @VenizelouE ,
I am writing here to confirm with you how thing going now?

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Answer 2

VenizelouE 1

Hi @Lucas Liu-MSFT
I haven't replied so far, as hybrid implementation has not proceeded since I asked the question (due to non-relevant to the project reasons).
I accept your answer (for which I thank you) but I cannot click on "Accept Answer" button as no such button is shown (no matter which browser I use).
Many Regards,
Evi

Lucas Liu-MSFT 6,191 Reputation points

2021-05-20T09:01:36.567+00:00

Hi @VenizelouE ,
Regarding you did not see the "Accept Answer" button, I think it is because you have changed the username of your account.

It’s good to know that my answer is helpful to you : )

Have a good day!

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Rule to filter out emails sent to EOL outbound connector (Centralized Transport mode enabled)

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