Hi support team,

I have a question about Exchange 2007 and Office 365.

We have Exchange 2007 to provide email service for our worldwide users.

One of our location would like to change use your Office 365 service.

For safety, they want us to keep their existings in Exchange server for a short period.

The problem was their domain will record to Office 365 for email server.

That means our Exchange server and Office 365 will share same domain in a short period for receiving emails.

This should have some conflicts because duplicate email address and their domain was registered in our DNS server.

It should caused our internal user cannot delivery emails to them.

Could you please help to check is it any setting or chance for Exchange and Office 365 work at the same time?

Thank you.

Best regards

Cary

Hi Cary,

Basis on your question, I recommend deploy migrate Exchange 2007 to Office 365.
Heres an article about it, for your reference: https://technet.microsoft.com/en-us/library/jj863291(v=exchg.150).aspx

Meanwhile, you will be clear about your worry by below blog :Microsoft Office 365: Make a Smooth Move to the Cloud.

Hi Cary,

Atricle suggested by Allen, should definately get the things done smoothly.

However you might be intersted to learn\refresh about "accepted domains, Authoritative and Internal Relay"

It should answer your question: "This should have some conflicts because duplicate email address and their domain was registered in our DNS server."

Basically, No there will not be any conflict for DNS domains. it will be handled by the Exchange Servers. Your public DNS points to single location either On-prem or O365 (On-prem in your case is better, as most of the users are here)

O365 way:

Internal relay Selecting this option means that recipients for this domain can be in Office 365 or your own email servers. Email is delivered to known recipients in Office 365 or is relayed to your own email server if the recipients arent known to Office 365.

• You should not select this option if all of the recipients for this domain are in Office 365.

• If you select this option, you must create an outbound connector; otherwise recipients on the domain who are not hosted in Office 365 wont be able to receive mail on your own email servers.

• This option is required if you enable the subdomain routing option on a domain in order to let email pass through the service and be delivered  to any subdomains of your accepted domains.

On-Premises Way:

Internal Relay Domain   E-mail is relayed to an e-mail server in another Active Directory forest in the organization.

An organization may have to share the same SMTP address space between two or more different messaging systems. For example, you may have to share the SMTP address space between Exchange and a third-party messaging system, or between Exchange environments that are configured in different Active Directory forests. In these scenarios, users in each email system have the same domain suffix as part of their email addresses.

To support these scenarios, you need to create an accepted domain that's configured as an internal relay domain. You also need to add a Send connector that's sourced on a Mailbox server and configured to send email to the shared address space.

Hi Satyajit,

Thank you for your help.

Is that means I need to enable Internal Relay at O365?

But how about On-Permises? I still cannot clearly understand for this method.

By On-Permises, I need to config at Exchange server side.

This may be hard for me to got the approve from management team.

Will enable Internal Relay at O365 more easy then enable On-Permises in Exchange server?

Sorry for my stupid questiong.

Regards

Cary

Hi Cary,

This is how you decide where to create the internal relay.

1. If outside emails to @yourdomain.com is hitting your Exchagne On-Premise server directly first : Create the internal relay here. Create a Send connector to forward the remaining emails to O365. O365 should have the Authoritaive domain entry, On-premise must remove it.

2. If outside emails to @yourdomain.com is hitting O365 server\IP directly first : Create the internal relay there. Create a Send connector to forward the remaining emails to On-Premise Exchange. On-Premise should have the Authoritaive domain entry, O365 shouldn't have it.

Basically for the outside world you are single either o365 or On-premises. The confusion and conflicts would be managed for the internal relay configur

Hi Stayajit,

Thank you very much for detail explanation.

May I clearly explain my question for the best result?

Actually, that location will use Office 365 for their main email communication after migrated from Exchange to Office 365.

But they want to keep existing Exchange email accounts for backup plan within a short period incase Office 365 cannot work correctly.

Finally, all email accounts located in Exchange server will be remove.

That means all outside emails will send to @yourdomain.com will go through Office 365.

But how about inside emails?

Because our Exchange server also DNS server was registered same domain name.

Could you please let me know the method that you provided to me can make our Exchange server understand how to handle all internal emails when sending to @yourdomain.com will automatically direct to Office 365?

Sorry for any confuse.

Thank you.

Best regards

Cary

Hi Allen,

As your reply.

I would like to ask for your confrm about below points.

1) You're not suggest to make Exchange email account at Office 365 work at the same time for same domain name

2) Is that really haven't method to fulfll Exchange and Office 365 work together with same domain name?

3)  The best way was remove all email accounts and DNS at our Exchange server and DNS server at the cutoff time so that Office 365 can work smoothly without any conflict with Exchange server and all internal emails can be recognize the status and send out to Office 365 as sending email to external.

Thank you.

Best regards

Cary

Hi Cary,

Q.Regarding your query on "Internal emails from On-Prem to O365" how does On-prem know where to send (internal or O365)

Ans. A critical component of making these two separate organizations appear as one combined organization to users and messages exchanged between them is hybrid transport. With hybrid transport, messages sent between recipients in either organization are authenticated, encrypted, and transferred using Transport Layer Security (TLS), and appear as internal to Exchange components such as transport rules, journaling, and anti-spam policies. Hybrid transport is automatically configured by the Hybrid Configuration wizard in Exchange 2013.

The Hybrid Configuration wizard configures all inbound and outbound connectors and other settings in this EOP company to secure messages sent between the on-premises and Exchange Online organizations and route messages to the right destination.

Enable mail flow between Office 365 and  Exchange INternally

If you have EOP and your own email servers, or if some of your mailboxes are in Exchange Online and some are on your email servers, connectors enable mail flow in both directions. You can enable mail flow between Office 365 and any SMTP-based email server such as Exchange, or a third-party email server. Create connectors to enable mail flow in both directions.

Mail Flow

https://technet.microsoft.com/en-us/library/exchange-online-mail-flow.aspx

Transport routing in Exchange 2013 hybrid deployments

https://technet.microsoft.com/en-us/library/jj659050(v=exchg.150).aspx

What I think it does in backend is create mailenabled users with @domain.mail.onmicrosoft.com as target address and @domain.com as SMTP additional. This way any email sent to the user gets redirected to the O365 domain.

Hybrid Routing Domain :

https://oddytee.wordpress.com/2015/01/27/troubleshoot-exchange-hybrid-mail-flow-with-office-365/

Hi Cary,

Q.Regarding your query on "Internal emails from On-Prem to O365" how does On-prem know where to send (internal or O365)

Ans. A critical component of making these two separate organizations appear as one combined organization to users and messages exchanged between them is hybrid transport. With hybrid transport, messages sent between recipients in either organization are authenticated, encrypted, and transferred using Transport Layer Security (TLS), and appear as internal to Exchange components such as transport rules, journaling, and anti-spam policies. Hybrid transport is automatically configured by the Hybrid Configuration wizard in Exchange 2013.

The Hybrid Configuration wizard configures all inbound and outbound connectors and other settings in this EOP company to secure messages sent between the on-premises and Exchange Online organizations and route messages to the right destination.

Enable mail flow between Office 365 and  Exchange INternally

If you have EOP and your own email servers, or if some of your mailboxes are in Exchange Online and some are on your email servers, connectors enable mail flow in both directions. You can enable mail flow between Office 365 and any SMTP-based email server such as Exchange, or a third-party email server. Create connectors to enable mail flow in both directions.

Mail Flow

https://technet.microsoft.com/en-us/library/exchange-online-mail-flow.aspx

Transport routing in Exchange 2013 hybrid deployments

https://technet.microsoft.com/en-us/library/jj659050(v=exchg.150).aspx

What I think it does in backend is create mailenabled users with @domain.mail.onmicrosoft.com as target address and @domain.com as SMTP additional. This way any email sent to the user gets redirected to the O365 domain.

Hybrid Routing Domain :

https://oddytee.wordpress.com/2015/01/27/troubleshoot-exchange-hybrid-mail-flow-with-office-365/