Manage the Migration to Exchange Online

In our last look at Exchange Online, we considered how to conduct a pre-deployment trial. If you’ve decided to move to
Microsoft Exchange Online, what’s your next step? Let me prep you for a quick tutorial on what
to do next, for a smooth migration to Microsoft Exchange Online.

Tools for Migration

For businesses, moving to a new system doesn’t mean a fresh start. IT needs to ensure that
data can be migrated from one platform to another; otherwise it will be a challenge for users
to get to work on the new system. In other words, migrating to a new system needs to be as seamless as possible for end users.

In an Exchange setup, data migration is possible if the IT infrastructure is using any of the following:

  • On-premises Exchange
  • POP3
  • IMAP

To do the migration, Microsoft has two tools available for us to use: Microsoft Online
Directory Synchronization Tool, and Microsoft Online Migration Tool. These tools alone are
enough for us to migrate from on-premise/off-premise Exchange, POP3 or even IMAP to Microsoft
Exchange Online/BPOS.

The Process

There are two phases when it comes to the migration: Moving the data (email) from the
old mail server to Microsoft Exchange Online; and the change of MX records. Let me break them

Phase 1: Migrate the data

Step 1. Directory Synchronizing (On-premise Exchange only): This step is just to run the Directory Synchronizing tool, keying in the credential for the BPOS and domain administrator’s account, and this tool will synchronize the local active directory user accounts to BPOS. This is straightforward and works 99 percent of the time. One thing to look out for, though: The tool will not install on a 64-bit server, nor Windows Small Business Server.

2. Microsoft Online Migration Tool: Using this tool, mailboxes from other servers can be copied to Microsoft Exchange Online. As long as the old mail server is running on either POP/IMAP, or on-premise/off-premise Exchange, this tool can help you migrate.

According to Microsoft, POP/IMAP migration will take at most 48 hours, for “a whole organization.” In my experience, even a small, five-person organization on a Xeon-based server can take over 72 hours, with CPU utilization constantly at 99 percent after a few hours of running the tool. On top of that, some emails don’t migrate due to malformed headers (according to the Migration Tool logs). Also, the emails are downloaded to the server running Microsoft Online Migration Tool before they’re uploaded to Microsoft Exchange Online, so low bandwidth means slow migration. This tool comes in 64- and 32-bit versions.

On the other hand, On-premise and off-premise (Hosted) Exchange migrations can be a breeze, with emails appearing on Exchange Online’s Outlook Web Access while the migration is still in progress.

In the end, you want to allow ample time for migrations, and you should try to do them in batches if at all possible.

Phase 2: Change the MX record

Once the emails are duplicated into the cloud (Microsoft Exchange Online), it is time to get
all emails routed into your new Microsoft Exchange Online’s mailbox account. How do you do that? Modify your domain name’s DNS MX record to:

Name Type Value MX 10

You should use a bigger value (than the existing MX record’s value) for Let the DNS propagate for 72 hours. Next, remove the old MX

Also, you might need to re-sync messages that went into the old email server due to
changes in the MX record. Some messages might get routed into the old email server due to
different Time to Live (TTL) values in DNS server configuration.

Exchange Online Back-Out Plan

If you think that migration needs no back-out plan, then you are wrong. Here are some basic backout steps you should plan for in case things go wrong.

If your email server supports migration through POP/IMAP (Microsoft Exchange Server):

  1. Log a Support Request to Microsoft Online Support to enable POP/IMAP.
  2. Use Microsoft Transporter Tools to download the emails from Microsoft Exchange Online to your on-premises Microsoft Exchange Server. You can download Microsoft Transporter Tools from here.

If your email server supports migration through POP/IMAP (non-Microsoft Exchange Server):

  1. Log a Support Request to Microsoft Online Support to enable POP/IMAP.
  2. Download the emails from Microsoft Exchange Online to your new email server, using your new email server’s migration tools.

If your email server doesn’t support migration through POP/IMAP:

  1. Archive the emails using Microsoft Office Outlook, just archive the data to a PST file. Note that you will need to do this on each individual email client.
  2. Re-configure email clients to connect to the new email server. Email clients will be connecting to an empty mailbox.
  3. Always plan to migrate back to a supported mail server.


Emails are a mission-critical application, so careful planning is needed.
When it comes to migrations for Microsoft Exchange Online, remember: Directory Sync, Microsoft
Online Migration Tool, and MX Record modifications.

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