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We are migrating from Exchange 2010 to Exchane online. Everything seems to going good so far, but we have an issue. Out local domain is conotosocorp.com, but our public/email domain is contoso.com. We have some Exchange contacts internally that point to alpha.contosocorp.com, but we do not own the public DNZ cone for contosocorp.com I know this gets confusing, but what happens is someone that has been migrated to the cloud all of the sudden cannot send email to the contact that we have listed as alpha.contosocorp.co,, because we do not own that public domain?
The issue is alpha.contosocorp.com is a contact for a SMTP server. So basically, I need to figure out a way to route email from office365 to a contact(internal server that it cannot route to publicly)
If anyone has any idea on this, let me know.
Not sure if I create s specific connector for that doain on-premises, if Exchange online will route to the on-premises server to handle that transport, or try to go there directly.
See my answer below on what you need to do.
Create an outbound connector in Office 365 for that address space ( alpha.contosocorp.com ) that smarthosts to an internal mailhost ( or Exchange Server with that as an accepted domain) (with an external IP and FQDN of course) and allow that from the EOP IPs on port 25 on your firewall. That internal mailhost will then need to know how to route to that internal contact.
You won't be able to have a contact in 365 with that domain suffix (alpha.contosocorp.com ) however if you dont own that domain.
https://learn.microsoft.com/en-us/microsoft-365/enterprise/urls-and-ip-address-ranges?view=o365-worldwide#exchange-online
40. 92.0.0/15, 40.107.0.0/16, 52.100.0.0/14, 104.47.0.0/17, 2a01:111:f400::/48, 2a01:111:f403::/48 TCP: 25
Thanks AndyDavid - That worked
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It's great that you can get useful information here. If you have other issues about Exchange, please feel free to post with related tags.
Have a nice day.
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Agree with AndyDavid. Since the alpha.contosocorp.com is not available from the Internet, we have to create a specific outbound connector to route emails to on-premises organization.
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Just checking in to see if above information was helpful.
Does the outbound connect work for you? If there is anything else we can do for you, please feel free to post in the forum.
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Any updates so far?
If you have solved your problem, could you share with us? Maybe it will help more people with similar problems.
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