Exchange cross forest communication

Your question is somewhat vague. Which version(s) of Exchange are you talking about? Do you want to know how you will set up the two Exchange organizations so they can communicate? Is this for two totally separate and different companies?
The exact steps differ depending on how you will do a migration.

Yes it is a general question.  How is the mail flowing between two different organization?

As far as I understand it. it is just SMTP for mail. If you want to see another companies free/busy, that is a little more complicated. It requires a trust, and permissions in each company's domains.

Right so say the trusts and permissions are established.   How does it see the free/busy and how does the mail flow between two different organizations.

That is really long answer. Once you have the proper permissions in each Exchange Org, the migration software handles all this. Of course there are a bunch of things to configure and it differs depending on the tools you use.
This is what I did. Go to Quest's web site and download the the Migration Manager for Exchange documentation. What you want to do is called an INTER org migration. Especially read the Installation Guide, User Manual, System Requirements and Access Rights and the Source and Target Preparation Guide for what Exchange versions you will be migrating. The link is here:
http://www.quest.com/migration-manager-for-exchange/  under the documents link, then go to Other.
Even though this is specific to Quest's software, it will give you a good idea of how the migration works. It is where I learned how to do Exchange migrations.

Hmm, I know the migration software handles that.  Either Quest, Priasoft, etc.   There is got to be another answer 'shorter' on how it handles that.

Honestly, there isn't a simple answer. Especially if you want free busy and an extended co-existence time. These situations are handled by the migration program (Quest, etc). The code in the program handles the more complicated tasks. I have never tried to understand the code. Just getting the program set up and working properly is a difficult enough task.
If you can do the migration quick enough, say over a weekend, and you are using 2007 or above, you can use the move-mailbox command to simply copy the mailboxes from one org to another. If you need the user accounts as well you can use ADMT.

Hmm, the reason I am asking.  I was asked the same question on one of the interviews and felt like the guy wasn't really pleased with my answer.  I kind of answered like you did.  I understand the software handles the migration.  There should be some kind of prerequisited to connect two together.  This is during the migration though.
Say you migrating users cross-forest.  How the people on the source email to people on the target?  The ones that hasn't been migrated yet.  How do the see each other's free/busy...

quote: Antknee869
If you can do the migration quick enough, say over a weekend, and you are using 2007 or above, you can use the move-mailbox command to simply copy the mailboxes from one org to another. If you need the user accounts as well you can use ADMT.

My understanding is that you simply cannot jump an Org with the move mailbox feature in Exchange.  The Org is the boundary,...and the Forest is the boundary of the Org.  Or perhaps Exchange can jump Orgs when moving a mailbox but the Orgs have to be in the same Forest?

Well I know I have done this using the software - Quest Migration for Exchange, Priasoft, etc.  But I still cannot the right answer.  How does the mail flow from one forest to another?  How does it see free/busy cross forest?  

Well I know I have done this using the software - Quest Migration for Exchange, Priasoft, etc

That is not doing it with Exchange,...that is doing it with 3rd party tools.  I cannot address 3rd party products.  I do not think Exchange itself will do this.

Exchange will jump the forest like that.How does the mail flow from one forest to another?

That same way it communicates with any other mail server out on the Internet,.....SMTP.  It is generic SMTP communication,..it is not regular Exchange-to-Exchange communication within the Exchange Org.

How does it see free/busy cross forest?

I don't think it does in the first place.

I'd be happy to be wrong,...but I think that is the way things are.

Over the Internet.  You are kidding right?

No.  Two Exchange Servers that are not in the same Org communicate with each other the same manner that they would communicate with non-Exchange Servers,...which is generic SMTP.  When they are not in the same Org they won't even know that it is another Exchange Server on the other end of the communication,...which is just the same way it is communicating with an AOL mail server when you send an email to JoeBlow@aol.com (hence my over the Internet comment)

Being in the same Org is how they "know" who and what each other are,...that is a large part of the reason an Exchange Org was invented.  If things are the same without an Org as with an Org then what is the point of having the Org?   We might as well go "Org-less" if we can enjoy all the same benefits without having it.

Interesting.
Say you need to separate one companay into two.  You build another environment.  Created trust-relationship.  Migrated Users, groups, computers, servers into another forest.  Associated the mailboxes with external accounts.  Next step is to migrate mailboxes onto the new forest.  I doubt it goes over the internet :-)

No one said anything was going over the internet.

I was making a comparison to communication methods.

Generic SMTP (just like what is used over the Internet),.....as compared to,.....the unique intimate type of communication that occurs between two Exchange Servers that are in the same Org together.

Cross-forest Exchange migtrations does not fly over the Internet.

NOBODY SAID THEY DID.


Just forget it,...you're clearly not going to get the point.

I got your point. Thank you!!

Nice answer!