Connect to two different exchange servers in two different domains from outlook 2016.

Connect to two different exchange servers in two different domains from outlook 2016.

We have old domain running exchange 2013, on olddomain.local.  We have exchange 2016 running on newdomain.local.  All computers are joined to olddomain and have email boxes that are  User names on the old domain are 123.

On the new domain we have domain users named abc, and email addresses that are  

The user names 123 and abc are the same person, they have one ID on the old domain and a different one on the new domain....don't ask me why it is a battle I fought and lost.

Currently the way things are configured is if you send a mail to it will go to 123's mailbox.  If you sent a mail to abc@public it will go to the correct mail box.  You can access abc's email via the OWA client.  If you log into a machine that is on the newdomain.local domain you will get outlook mail that goes to abc's user.....all that is working correctly.

What I would like is for the users on the olddomain to have access to their email on the new domain via outlook and not the web client.

I have checked this case:

And for some reason I can't get it to take the user ID or password for the new account....the same issue the OP had in the 3rd post...but can't get it to take the user name/password.

My setup I think is the same as his....two different domains, two different exchange servers, mine are a 2013 and a 2016.  

I am working on several issues with this email box so I will likely be posting a few questions on this in a few threads.
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AmitIT ArchitectCommented:
Answer is not possible. Exchange org is tied to only one forest. You cannot access Exchange in another forest, until you setup up linked mailbox concept. Or we call it resource forest concept. More to read here:

For your situation OWA is the best bet.
Alexei KuznetsovMicrosoft Outlook MVPCommented:
Your case works perfectly well in my office. We have two domains and two Exchange Servers. The only thing I had to do is to configure DNS: on primary domain's DNS server I've added second domain's DNS as a first forwarder. Of course, you neeed to have .local autodiscover configured properly in order to connect the account to Outlook 2016 and type other domain's username in Outlook (when asked) in the DOMAIN\user format.

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SilverwolfSenior Server EngineerCommented:
Alexi is correct, just need to make sure that you have Autodiscover configured properly.

I also have a similar setup in my office. The users system are on one domain and the email was migrated to the Exchange Farm on the other domain...both in completely separate forests with a 2-way trust. We had to setup new profiles in Outlook of course. In fact during the migration, we had 2 profiles setup for the user, one to their old mailbox and one to the new one in the new domain.
Alexei KuznetsovMicrosoft Outlook MVPCommented:
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