Force Exchange to send email outside

[JHNN3791]

Hello,

I currently have 2 accounts for 2 companies in Exchange 365. domainA.com & domainB.com

I would like to add domainB.com to the domainA account in order to have something to unify.

So I added a second domain in my account A and I created the TXT in the dns but I have not yet change the MX. Users are not yet creating on domainB because I have to migrate the old exchange.

The trouble is that when adding the domainB in domainA, exchange sends the mail inside and so when paul@doaminA.com sends to peter@domainB.com, the sender receives an email like what the user does not exist. => Logic they are not yet create

To put it simply, I would like to force exchange to send mail to the outside more than to relay it internally.

Thank you  in advance for you help.

[#2]

You need to configure a relay on the domain! Exchange route mails internally first instead of using the MX record!

http://guides.appriver.com/m/8585/l/144618-enable-internal-relay-domain

/ Adam

[#3]

Hi @JHNN3791 ,

You can create as the following.

1. Connect to Exchange Online PowerShell.
2. Create the Distribution List (DL):
   New-DistributionGroup -Name "NotMigratedUsers"
3. Add All Users to this DL.
4. Create the Connector:
   $result = New-OutboundConnector -Name "OnPremConnector" -ConnectorType OnPremises -SmartHosts "<fill smart host to source environment>" -UseMXRecord $false -IsTransportRuleScoped $true
   • -SmartHosts entry needs to be set to the URL or IP Address of the Source environment server.
5. Create Rule:
   $result = New-TransportRule -Name "Pilot" -SentToMemberOf "NotMigratedUsers" -RouteMessageOutboundConnector "OnPremConnector"

When a user is fully migrated, remove the user from the DL, and they will receive their email in their own Office 365 mailbox.