I am managing a small business IT environment which includes an on-premise Exchange mail server. Now a few users would like to move to Office365 to be able to work from anywhere (emails + OneDrive mainly).

I found outdated doc from MS but nothing recent. So is there a way to have both coexist in an organization ? What type of setup should I look?

  • You’re looking at Exchange Hybrid. There should be plenty of documentation to support this configuration. Might answer properly if I get a moment but that will get you started. – Rob Moir May 11 at 12:34
  • It’s worth noting that even a hybrid migration from plain exchange is a BIG job. Have you thought about just showing them how to get their devices to see the mail server (surely they can already get mail on their phones / devices?). Then maybe think about setting up RDS if you have the resource capacity. I know you’ve mentioned resource is limited but not how limited. – Timothy Frew May 12 at 16:25
  • Thanks @TimothyFrew, indeed I’m afraid the Hybrid setup may be too much work. They have a standard Outlook on their work computer, nothing on their devices. – ack__ May 12 at 16:30
  • Is it setup with auto discover and other relevant DNS records as well as firewall configurations to allow non work machines to receive mail? I would do that personally – Timothy Frew May 12 at 16:32
  • Then you can also look at using something like sharepoint which may be better than one drive – Timothy Frew May 12 at 16:32

Maybe tell us exactly what you'd like to do. When you say these users would like to "work from anywhere" what do you mean exactly? Why can't they use their email from anywhere now?

You don't need to move their email to Office 365 for them to have OneDrive, you just need an Office 365 subscription. You don't have to move anything.

As for email, you could move their mailboxes to Office 365 using a Hybrid migration, but why can't they work with their email from anywhere right now? What's stopping them?

Based on your comment to my comment:

You can implement Azure AD Connect to synchronize your on premises AD to Office 365, then you can configure an Exchange Hybrid configuration and move these mailboxes to Office 365 and enable MFA for these users in Office 365. You can purchase the appropriate subscription for these users and leave all other users without a subscription until you're ready to move them to Office 365. That way you're only paying for what you need.

  • Ok so basically, the objective is that for a few users (3 at this point), they are able to: 1) access their emails from any device / network using 2FA to login. 2) access and share their documents from anywhere too (hence OneDrive). 3) Progressively get rid of their on-prem systems and move to a cloud-based setup (reasons here are not technical but more business/political). – ack__ May 11 at 14:42
  • I agree for OneDrive - it’s more an example I gave but indeed that’s the easy part. – ack__ May 11 at 14:43
  • I certainly understand that what I ask could be done using only MS Exchange but this is not really an option. The Exchange server is managed by a 3rd party who will not be able to change the current configuration too much (today there’s no Web Access for outlook, and users can only access their emails using their business laptop - from any network though) – ack__ May 11 at 14:46
  • And finally - the overall setup needs to be « out of the box » as they have very limited IT resources and skills. They can’t afford to re-configure Exchange or change their licence plan to enable features such as Web access etc. – ack__ May 11 at 14:48
  • It's not entirely clear to me what the current restrictions and limitations are. Who owns the existing Exchange server? Where is it located? – joeqwerty May 11 at 15:26

For your request, hybrid deployment is the option. As Timothy said. Hybrid is big and complex job. Since there are few users, you could consider moving all to Office 365.

Exchange Deployment Assistant https://assistants.microsoft.com/


You can setup your external mail flow to enter your org through Exchange onprem and get routed to the Office 365 tenant only for those mailboxes you want to bring onto the cloud. You then have to setup an internal mail flow from Exchange onprem to O365 so that internal onprem senders can send to the mailboxes online. O365 mailboxes will use Exchange online to send their emails.

So: Manually enable hybrid mailflow keeping your Exchange as MX/smtpout: Configure your domain as internal relay on the Exchange Server so that it may relay emails to the addresses migrated to o365. Create a TLS send connector back to Exchange online scoped to your whatever.mail.onmicrosoft.com domain. Convert the users you need to migrate from mailboxes to mailusers populating their targetaddress attribute with office365 whatever.mail.onmicrosoft.com address. You may also create on o365 an additional authenticated send connector back to the on prem Exchange scoped as yourdomain.whatever to keep the mail flow to and from your users (onprem and O365) internal.

This is a general procedure, your environment will probably need some adjustment.

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