Exchange on-site to office 365

ZeeK used Ask the Experts™
Hi guys.

I am moving to office 365 E3 from existing exchange on-site. During the move what is the best way of not loosing any emails. Note, I will not be migrating at this stage and planned migration for later and pst for all accounts are already backed up.
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Tej Pratap Shukla ~DexterServer Administrator

Hello ZeeK,

You can migrate On-premises mailbox to the Exchange Online.
Please follow the steps given below:
1) Open the Exchange Admin Center, the go to Office 365 >> Recipients >> Migration.
2) Click the Add Icon, and then choose Migrate to Exchange Online.
3) At the Select a migration type page, choose Remote move migration and then select Next.
4) At the Select the users page, click the Add Icon and select the on-premises users to move to Office 365 and click Add and then choose OK. The select Next.
5) At the Enter the Windows user account credential page, enter the Exchange on-site admin account name in the On-premises administrator name text box and enter the admin password for this account in the Exchange On-premises administrator password text box. Then click on Next.

To know more about the procedures, you can go to the link below:

Also to know about cutover migration to Office 365 (Exchange Online) you can follow the link below:

I hope this works for you!

Best Regards,
Tej Pratap Shukla
Marshal HubsEmail Consultant

Please take a look at different migartion methods:

Cutover Migration: You can use this method if you have fewer than 2000 mailboxes. This method is supported for Exchange 2003, 2007 and 2010:

Staged Migration: You can use this method if you have more than 2,000 mailboxes:

Hybrid Migration: If you have Exchange 2010/2013 and more than 150-2,000 mailboxes, you should use this method:

Microsoft provides two helpful tools for planning migration, including Exchange Server Deployment Assistant, this tool give step-by-step instruction for greenfield deployments, coexistence deployments, and migration-focused deployments. Second tool is the Remote Connectivity Analyzer that lets you test your connectivity.


Hi guys as said I need to activate emails at office 365 and need to migrate at later stage. Regarding the question is referring to incoming emails for downtime. What's best to not loose the new emails?
Associate Consultant
Hi Zeek,

I would suggest you to have at least 2 MX with different priority (one with lower priority to pointing to EOP-Exchange Online Protection and Another with higher priority pointing to your On-Prem Mailing solution).

During transition of MX pointer change at ISP level, some mails would be delivered to both mailboxes; however, once the MX is pointed and replicated to EOP you will directly receive mails on Office 365 mailbox.

This provision would ensure that there is no mail/data loss and migration is smooth.

Note: I would suggest you to take the PST of all accounts before decommissioning the on-prem mail server after moving your MX to office 365 as there might be some mails which will be delivered to your on-prem mailbox during these changes.

Aanand Singh Karki

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