Disable Mailing for O365 domain

[David1595]

Hello there.

I have trouble with o365 in connection with our existing mail system, and for whatever reason the ms support is not able to help me.

I thought maybe here someone can help me.

I have a default O365 domain "company.de".

In the DNS Setup of the domain in 365 admin center "exchange", "Skype for Business" and "Basic Moblity and Security" is not ticked.

The 365 username of all my users is for example "user1@company.de".

When someone sens for example a MS Teams meeting invitation to user1@company.de the user receives the mail at https://outlook.office.com/mail/inbox

HOWEVER I run an own email server on premise.

I want that the 365 mails are sent normally via my mx record of "company.de" to my mail server on premise.

But I do not know how I can tell 365 that it should not process any mail for "company.de".

Sorry for my english

maybe someone can help

[#2 · Accepted solution]

If you have a cloud mailbox created for the user, messages will be delivered there by default. Is there any particular reason why you have created mailboxes in O365 if your mail system is on-premises?

[#3]

Hi David,
There could be several solutions depending on your requirements.
Microsoft has a article on mail flow best practices, maybe this can guide you to a solutions.
https://docs.microsoft.com/en-us/exchange/mail-flow-best-practices/mail-flow-best-practices

At first I would say it is the MX record in DNS. Did you add <MX token>.mail.protection.outlook.com with a higher priority than your company.de MX record?

Regards

[#4]

@David1595 

Can you validate which mail flow scenario you currently see via message headers?

Are you saying the current mail flow looks like this:
Internet>MX>O365 Mailbox? 

Or this:
Internet>MX>On Premises>O365 Mailbox?

Do you want O365 mailboxes to receive mail at all?

Do you want mail to be processed by on premises servers prior to being sent to O365?

Is the on premises server new? 

[#5]

Thank you.

As we use primarly HCL Domino I was not aware that when using AD Sync and give the users exchange online licenses a mailbox is automatically created.

I now created a "internal relay" with a connector and when I remove the "exchange online" license there is no mailbox and the relay is used and the mail is delievered as I want.

Thank you all for your time. I am sure others with the same problem will see this thread and solve it.