Exchange 2010 - Federation Trust to see other organisation's GAL?


I've just created a two way forest trust between my company and a company we are in process of acquiring

At the moment the only requirement for mail is that we have a shared mailbox hosted in Exchange 2010 on prem at my company which we need to give the acquired company staff access to

We don't plan on migration as such, they will eventually move across to our site and use my company mailboxes - we will archive their existing mailboxes to PST

What is the best way to achieve visibility in Exchange just now? Federation trust, then set up an Organisational Relationship?

The acquired company's Exchange is hosted - would I need to get them to do the federation trust part on their side too?  I assume this is the case because what I've read refers to the Microsoft Federation Gateway, which again I assume both organisations need to be configured to use?

Thanks in advance

Jason MIT Systems AdministratorAsked:
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According to the documentation on sharing, if I understand it correctly the vendor would need to follow the same steps in his organization for "".
Jason MIT Systems AdministratorAuthor Commented:


So there would need to be the TXT record in both organisations DNS to act as a broker for the connection, if I understand the process correctly?

TXT record is used for validation, pretty much in the same manner as if you would do Federation with Office365. Simply follow the setup documentation.
Jason MIT Systems AdministratorAuthor Commented:
I'm going to close this because I figured by using Outlook 2013 and pointing it to our mail server, I can get past Outlook 2016 trying to autodiscover external FQDN URL's - whereas we use internal.

So Outlook 2013 lets me add the shared mailbox fine

Thanks for your comments

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Jason MIT Systems AdministratorAuthor Commented:
it allows me to do what I need to do
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