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Exchange 2003 to Exchange cloud

We have an Exchange 2003 and we plan to migrate users to Office 365 cloud.

If I setup my domain on Office 365 (ie. add records to my DNS), does it mean all my mails will route to Office 365 and my users can't receive the email on my Exchange 2003 ? Does it mean user can't send / receive email unless they configure their account to cloud ?

What's the best way to migrate Exchange 2003 to cloud in my stituation ?

We have a blackbbery but we don't want to keep it. Any option to handle those BB users after moving to cloud.

Any solution to backup the users mailbox in cloud back to local storage ?


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8/22/2022 - Mon


you can setup your domain on o365, create users, groups, rules, etc, but do not reconfigure MX record until you finish all of that.
Since exchange 2003 is not supported for hybrid, then only way for your users to receive email both to exchange 2003 and o365, would be for MX record still to point to exchange 2003. You would then create forwarder that would forward email to o365, via address such as username@company.onmicrosoft.com.
Every user will always have first email address in that format, so by using it, you would be able to have email on both platforms.

I would just migrate users to o365, and reconfigure their Outlook. One by one..if you don't have to many users?


I did this just less than a year ago. O365 has a migration routine build in to the admin console. It will automatically add accounts to O365 based on the email accounts in your 2003 Server. It will than do a one directional sync from your 2003 Server to O365. This sync will be continuous until you stop it. Ivan is correct. Do not change your MX record yet but you can start moving people's Outlook over to O365 while this sync is running. Mail will come in to the 2003 Server and immediately (OK maybe not immediately but quickly) be synced to O365 and be available via everyone's Outlook.

   Then on a slow weekend you can change your MX record and it will be transparent to the users. Let the sync run for a week after changing your MX records to catch people that don't pick up the MX change right away. After a week you stop the O365 sync and everything should be a done deal.

#1 Do you mean auto-sync for AD account, not the email ?
"It will automatically add accounts to O365 based on the email accounts in your 2003 Server. It will than do a one directional sync from your 2003 Server to O365." Any more info on auto-sync ?

#2 Do you mean each user will setup a profile to cloud @company.onmicrosoft.com and setup forwarding rule in Exchange 2003 to cloud email ? How to ensure outgoing emails still use the company email domain ?

#3 After changing MX record in my DNS and setup the primary domain in cloud to my company domain, do I need to reconfigure each client's outlook profile again ?

#4 any solution for backing up user emails on cloud ?
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Go in to Exchange Admin Center and click on Migration (under Recipients)

1) It is very similar to Auto Sync but not exactly the same. It is very simple. You tell it where your 2003 Exchange Server is. It will connect to it in some ActiveSync method. Import all the email accounts first and than go back and import all the email for those account. I think it is technically a uni-directional sync.

2) It has nothing to do with forwarding. If you Outlook is still set up to connect to your local Exchange Server it sends via that Exchange Server. If your Outlook is set up for O365 it send via O365. That is the beauty of it. You have all the time in the works to move you user's Outlook over to O365.

3) You need to set up you domain on O365 first. Otherwise you won't be able to log in and get to the migration. Log in as a admin. Don't add any users. Go right to the migration. It will scan your 2003 AD and add the users and their email addresses for you. It will thin start importing email for those users. The import (it is actually a sync) so the sync will repeat until you tel it to stop. Any time email comes in to your local Exchange Server is is synced up to the same user in the Cloud.

4) Yes but I forget what it is called. I came across it here on EE. I am sure if you Google it you will find many.


#3 Actually, I want user to keep using @mydomain.com after moving to cloud. Does it mean I don't ActiveSync to sync Exchange 2003 email to microsoft cloud account .

My concern is after setting up the primary domain in cloud to my company domain and permanently change the MX record, will previous setup profile in Outlook (pointing to @company.onmicrosoft.com) need to reconfigure again (as now it is pointing to @company.com in cloud) ?

The email addresses stay exactly the same. Technically O365 logs in to your Exchange Server via ActiveSync but it needs administrator credentials. It than looks through all the Exchange Mailboxes to build the O365 user list and then syncs all the email in the local Exchange Server to the Cloud accounts and continues syncing until you tell it to stop. So let the sync run until you are done changing everyone's Outlook over to access their cloud accounts and through the changing of your MX records than add 7 days. It really doesn't hurt :)

   Not sure I understand the second part of your question. Right now everyone's Outlook is set up to access the local Exchange Server isn't it? You really don't set anything up to point to @company.onmicrosoft.com Your email address now is user@company.com and after the migration it is still user@company.com but you change the Outlook Profile from point to user@company.com on the local Exchange Server to point to user@company.com in the cloud.

   You immediately change your DNS records (with the exception of the MX Record) the way Microsoft want it (to point to the cloud). All your user's Outlook still points to the local Exchange Server just as always. Then, one by one, you change the Outlook to point to the cloud instead of the local Exchange server. The easiest way to do that is to delete the current Outlook profile and when Outlook starts walk it through the automatic setup based on autodiscover (which is one of the DNS changes you make right away).
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Before actual migration, Outlook will have only outlook profile to Exchange 2003 and a new profile to Cloud (@company.com in cloud). User can recieve mails from both domain separately through their profile.

After migration (attached file). Can users receive company.com domain on their cloud profile setup in Outlook ?


The thing about doing the migration with the continuous sync is that there is no need for multiple profiles. It would probably confuse the users more then it would help them.

As we need keep using the company domain, rather than "company.onmicrosoft.com", is it necessary to change the my company domain DNS as shown in the attached file or there are other better way to handle this ?

My plan is
1. setup up onmicrosoft.com in each workstation
2. setup MX, TXT record in company domain during the weekend
3. reconfigure each client profile again

Any comment ?

Thx again.
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