Forum Discussion
Adding a new domain (company acquisition) to existing Office 365 Environment
Hi,
Our company ( hybrid, 600 E3 users) acquired a company ( calling it X 200 user exchange 2010) my question is when is the right time to add the domain name X.com to our office 365 environment.
we tried to add and confirm the ownership of domain with TXT it without changing MX records and we couldn`t sent out emails to someone@x.com anymore.
I really appreciate if someone can list the major steps.
Thanks
When you add the domain, you need to make sure to configure it as Internal Relay in Exchange Online. Otherwise, for any address associated with that domain, Exchange Online will attempt internal delivery, and will fail if no matching account was found. When you set the domain as Internal relay, it will still check for internal matches, but if no such are found it will redirect the message to where the MX record points at currently.
- VasilMichev , is this required when you have set no exo licenses for those users ?
adam deltinger license is not a requirement generally speaking, as you can have valid Exchange recipients even without a license. But if a matching recipient exists, ExO will always try internal delivery first.
Connector might not be needed as well, depending on the configuration. And after all 200 users isn't that much, you can probably do the migration over a single weekend, and avoid dealing with complicated setups.
- AysaniCopper Contributor
Hi Vasil,
Thanks for your reply. I was reading this documentation for the type of connectors
could you please point me out to the right one?
So although no DNS record was changed, just the TXT record added to domain ownership approval, and no service was enabled for the new domain it was an expected behavior?
T
- Hi!
Vasil is right. Unless you add a send connector and set the domain to internal relay then if the existing users on 365 send mail to that domain it’s going to look internally within Office 365 and bounce.
So,
1./ Add domain, txt and validate and add the Exchange service, do not change any other DNS records
The domain goes onto Exchange Online at this point. If you don’t do steps 2 and 3 you may start experiencing bounce backs if users send mail from the existing users to the newly added domain. This is expected behaviour.
2./ Go into Exchange Admin Console and in Accepted Domains change the newly added domain to internal relay domain
3./ In The Exchange Admin Console Add a outbound connector (from Office 365 to the existing mail platform) for the newly added domain pointing to the highest priority MX record on that domain.
https://docs.microsoft.com/en-us/exchange/mail-flow-best-practices/use-connectors-to-configure-mail-flow/set-up-connectors-to-route-mail
That should work and ensure mail flows back to the new domain’s mail platform from Office 365 users.
You may want to do this change out of hours or notify the existing 365 users so they do not send mail between the domains at the time you make these changes.
Hope that helps
Best, Chris
- It should be possible to add the domain but not altering the dns records for mail!
What are you trying to accomplish? Are you adding the users to your tenant, migrating mailboxes?
Generally:
I’d make sure everything like users from x is set up with the @onmicrosoft domain and mailboxes migrated if that’s the case, then add the domain and change dns records!
Don’t add the exchange license to the users still having their mail on premises in exchange 2007!- AysaniCopper Contributor
Thanks Adam, so if I understand correctly you are suggesting to :
1- have a trust set up between domains
2-sync the users in X domain to O365 using Adsync
3-Add the X domain to O365
4- migrate the mailboxes to O365
will this prevent the issue that already happened?We were just trying to confirm the ownership of the x.com in O365 and we weren't able to send emails out to x.com anymore.
Thank you
- Hi! If you’re just trying to accomplish the latter see @Vasils post!
Otherwise I suggest you find a third party migration tool, there’s a few great ones and do a migration! First before changing the domain and dns! That way the users work as usual and have their mailflow the same! You don’t necessarily need to migrate the users, but rather create the users in your tenant then match their accounts with their mailboxes!
It all depends on your exact scenario
Adam