Searched forum but couldn't find anything closely related.  Just became more confusing.

Scenario: Company A split into two, and now we have Company A and Company B (same network, subnet, etc.) but we've put them on their own DC and Exchange. Previously Company B's MX was pointingto Company A so that their domain could receive email through Company A's server. I've changed Company B's MX record to now point to their new Exchange 2013 server.  Almost all mail flows as it should internal\external, inbound\outbound except for CompanyA's internal to Company B's internal.  I found the article below and there is in fact a mail relay set up in Company A's Exchange 2010 server.  Link: http://support.microsoft.com/kb/2741195/en-us.  But I'm also seeing it listed as an Accepted Domain under Org. Configuration->Hub Transport->Accepted Domains.  So my question is, where do I remove or modify the entry.  I've tried tochange the Accepted Domain to Internal and External Relay Domain but then it breaks the other way (Company B sending to CompanyA).  Any help would be appreciated.

Thank You-

Dan

Just to review.  Company A's email goes in and out of Company A's mail server.  Company B's email goes in and out of Company B's mail server.  So neither company relays external email through the other's server correct?  If that is so, you will want to remove Company B's email domain from the Accepted Domains in Company A's servers.

To send email to Company B internally, create a new send connector with these settings (on Company A's mail server):

1) Type = Custom
2) if you have a DNS record defined then use MX record.  If you do not, then use route through smart host and add Company B's mail server as the smart host.
3) For address space, enter Company B's smtp domain here.  Cost of 1.
4) Add company A's mail server as source server. and finish.

Then test mail flow.  If it does not work, then you may have to allow Company A's mail server IP to relay on Company B's mail server.  To do that you need to add the IP to your application relay connector (Mail Flow - Receive Connectors).

Let us know if that works.

You are correct.  Company A now only sends its own email (Exchange 2010) user@companyA.com and Company B now only sends it own email (Exchange 2013) user@companyB.com.  I just have one more question.  Is adding that connector just in case we lose internet (WAN) access?  So if I don't add that connector mail will still flow between the companies, but not if we lose internet access.  Or will it break if I just remove Company B's accepted domain from Company A's Exchange server?  The reason I ask is because we only have a live environment (no dev\test) but I'd like to make the change now (accepted domain removal) and then add the connector later for testing.

Thank You Again-

Daniel

If you remove the accepted domain and remove any connector with that domain defined, then email to Company B from Company A will route to the internet.  That might not be the most efficient way to do things and having a connector will certainly make mail flow go faster between the two domains.   That part is up to you.

Thank You-

I will have to wait until tonight to try it as I don't want to bring anyone down right now.  Will update with what happens tomorrow

Daniel

Sounds great.  If it works, don't forget to mark your question answered.  If it doesn't, let us know what happened.

Ok so took a leap of faith and tried it.  Here's what I had to do for those in the future.  I'm sorry I should have mentioned this error earlier that I was getting but forgot about it. ERROR "s referenced in an e-mail address policy by the proxy address template "  So I searched and it seems I had to go through our Default Email Policies (Org-hub transport-email policy) and run through the wizard to get rid of their domain. Then I just went to the Accepted Domain and was able to delete it. Everything seems to be working now.  So JAUCG you were right that all I had to do was remove that Accepted Domain (after I figured out that I had to remove that email policy domain first).  Thanks again and marked you as the answerer - Daniel