Link up two exchange servers from two different domains/forest

Hello Experts
we have a new project our company bought another small company.
we have our own Active Directory and exchange 2010 setup

new company have there own AD and Exchange 2010 setup.

we use   as our email domain to send recieve emails.

we want new company exchange server to send/recieve emails as  

how we can do this.
how to link to exchange server to talk to each other for routing mails for users across each server.

this is temp setup as we will later bring them all on our exchange server.

Many Thanks
H-SinghTechnical DirectorAsked:
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This is what i did on my previous task.

1. Make sure both DNS able to ping each others
2. Create a forest trust
3. Create a AD account for user from new company in your AD
4. Move the mailboxes for user from new company to your mail server
BusbarSolutions ArchitectCommented:
I would disagree with the above suggestion, you will have to setup shared SMTP namepsace not forest trust, here are the steps

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H-SinghTechnical DirectorAuthor Commented:
thanks Busbar i looked into that article and that looks the way forward. just to clarify few things.

i will need to change my main accepted domain on First server to Internal Relay Domain.

and create send connector for this domain to use Second Server as Smart host.

not sure what exactly i need to do on second server.
will this be accepted domain or internal relay and create one connector back to First server.

how user will send email to internal users.
i think i better start testing with one of my test domain.

H-SinghTechnical DirectorAuthor Commented:
looks like i got it working. but am not sure if it will cause loop etc. for incorrect email IDs on given domain. as each server sending to second one if it can't find the mailbox on local server.

i added  as authorative domain on both exchange servers.

created send connector for *  on both exchange servers on first its using IP of second server as smarthost.

and on second server i used IP of first server as smarthost in send connector.

tested emails across , all working.

but not getting any NDRs for incorrect email IDs.  

but thanks for the advise
H-SinghTechnical DirectorAuthor Commented:
thanks guys,  i found some further detailed links via your given links and manage to make it work for me.
H-Singh Wish you would have shared the additional links. I'm getting ready for a migration and need all the help I can get.
H-SinghTechnical DirectorAuthor Commented:
Hi abustraan
I will try to put up solution together for you what I did as it's been bit time now

I had it working then we moved their users to our AD later on
Thank you.
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