Here is my scenario: Our internal domain is mycompany.corp. Our external domain is mycompany.com. Our current MX record for mycompany.com is hosted a 3rd party solution which we POP/SMTP to. We have installed our Exchange 2010 environment. We created a subdomain called exchange.mycompany.com and an MX record for this. For our testing, we are using our "fire" accounts, which are part of the mycompany.corp internal domain. When I send an email from user@mycompany.com through the third party provider that hosts our email to user@exchange.mycompany.com, it will reach the Hub Transport, it is coming back as being undeliverable and then disappearing from the queue. No NDR is being sent. Any ideas why this is happening?

Its its coming back as undeliverable, then you are getting a NDR. What exactly does the NDR say? And what does message tracking show on the Hub?

Hi DBA Did you check what A_D said? You can first search the Message Tracking Logs, please refer to http://technet.microsoft.com/en-us/library/bb124926.aspx Cheers Zi Feng

Hi DBA Any update on this issue? CheersZi Feng TechNet Community Support

Did you tell Exchange that it should accept email for the EXCHANGE.mycompany.com domain or the child domain ? Configure Exchange 2010 to Accept E-Mail for More Than One Authoritative Domain http://technet.microsoft.com/en-us/library/aa996314.aspx When you create an accepted domain, you can use a wildcard character (*) in the address space to indicate that all subdomains of the SMTP address space are also accepted by the Exchange organization. For example, to configure Contoso.com and all its subdomains as accepted domains, enter *.Contoso.com as the SMTP address space. However, if the subdomain names will be used in an e-mail address policy, each subdomain must have an explicit accepted domain entry. Cheers, Rhoderick

Sorry for not getting back to everyone sooner. It turned out to be the Authoritative Domain issue. I had not added the wildcard or the actual subdomain record to the authoratative domains. Once done and once the subscription was updated, there were no problems receiving mail for the test account. When we go live with this with company.com email addresses, I'll add the wildcard one as for now I've added only the one single subdomain.