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I'm setting up SMTP namespace sharing between two different Exchange 2010 organizations/forests that are connected via an AD trust.

I'm using these 2 articles as references:

Configure Exchange to Route Messages for a Shared Address Space

Configure Exchange 2010 to Accept E-Mail for More Than One Authoritative Domain

My questions are:

  1. Do I need to setup the same on both sides? Meaning on the second Exchange org do I setup it as an internet relay as well and create a send connector BACK to the first Exchange org? It doesn't mention this, and seems like it would cause a loop but I'm not sure.
  2. The articles seem to cover mail delivery but what about sending? Two sides here: a) how does mail from ExchangeOrgB send FROM the shared namespace? Out its default send connector? Or does it need to route it back to ExchangeOrgA to send out? b) what about email between the two Orgs? If ExchangeOrgB's mailbox "" tries to send to ExchangeOrgA's mailbox "" what path does it take? It would seem ExchangeOrgB would need a send connector in this case and be setup like ExchangeOrgA, yes/no?

Hopefully someone here has done this...otherwise I'll contact MS for clarification and update my blog... :)

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I provided this link in another question that goes over the process (it covers dedicated to hosted, but may still help).

I haven't personally set this up, but I think the fact that you're using a subdomain for inter-organization message routing is what keeps you from creating a loop.

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