For one of our customers we are currently working on a prove of concept to implement on premise exchange servers. The problem mentioned below takes place on test servers.
Server names and mail domain names are changed to generic values.
On our on premise exchange environment we encounter the following problems when emailing to a specific email domain .
Email to the domain companyname.com is placed in to the Unreachable Domain queue with the following error:
Last Error: The mailbox recipient does not have a mailbox database
Queue ID: SERVEREX01\Unreachable
Recipients: user@companyname.com;2;3;The mailbox recipient does not have a mailbox database;1;<No Home Database>
Situation:
Customer uses a local Active Directory which contains all the user accounts and uses Office 365 / Exchange Online to provide these users with a mailbox. SSO between the local AD and O365 is provided by a third party identity provider. Dirsync is used to sync all user information from the local AD to O365 AD. This also includes the SMTP addresses users have on the Office 365 mailbox. In the local AD this information is saved is the proxyaddress attribute field and synced to O365. Office 365 uses the following mail domains for customer: companyname.com and companyname.onmicrosoft.com.
Customer wants to use local on premise exchange servers for specific locations and users and doesn’t want to implement a hybrid exchange environment. Therefore we installed an Exchange 2010 Edge server in the DMZ and an Exchange 2013 MBX / CAS server in the server network. The Exchange 2013 server is installed in the same Active Directory as the one mentioned above. This environment uses the mail domain @central.companyname.com. The email environment is configured to only accept email for this domain.
The email environment works fine. It can send and receive email internally and externally. There is only one issue. It’s impossible to send email from the on premise environment to office 365. The other way around (O365 to on premise) works fine.
When an email is send to a companyname.com email address the exchange 2013 mail server places the email in the Unreachable Domain queue and reports the following error:
Last Error: The mailbox recipient does not have a mailbox database
Queue ID: SERVEREX01\Unreachable
Recipients: user@companyname.com;2;3;The mailbox recipient does not have a mailbox database;1;<No Home Database>
This is caused by the fact that the @companyname.com email addresses are stored in the active directory exchange uses. We tried to fix this problem to create a internal and external relay domain with the appropriate send connector but this didn’t help.
When we remove the proxyaddress attribute in the local active directory we are able to send email from the on premise exchange server to Office365. Removing the proxyaddresses is not a solution because these settings will be synced to Office 365 and users can’t receive email anymore in there cloud mailbox.
It looks like the SMTP Categorizer first looks in active directory if the target email addresses is available. If so it will send the email to this users (but doesn’t have a mailbox server and mailbox database).
Can we configure a working mailflow for email from on premise to Office 365 for @companyname.com addresses?