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We have preformed a minimal hybrid migration.

Migrated a few test mailboxes.

We have a few 100 to go.

We would like to ensure that our 3rd party email spam filter is used for onprem mailboxes and online mailboxes.

Is this possible during the hybrid migration or would we need to wait until we have migrated everyone and updated the MX record.

Steve Drake
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2 Answers2

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If your MX record points to the on premises Exchange server or to the 3rd party spam filter and is then delivered to the on premises Exchange server then nothing should change. Email destined for mailboxes that have been migrated to O365 will be routed to your existing MX record and will then be routed to the O365 mailboxes by way of your on premises Exchange server.

joeqwerty
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I think you could keep the MX record pointing to 3rd spam filter if you need. It is not necessary to change the MX record to point to O365, it could have different scenarios. Incoming message could be delivered between O365 and Exchange on-premise. Here is a good article: https://practical365.com/exchange-server/mx-records-for-exchange-hybrid-deployments/

Shaw
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