I have forest trust established between forest A and B. Exchange is installed in forest A. My query is that my users in forest B will login to their computers joined to forest B with their forest B credentials. They have mailbox created in forest A and login to outlook using  forest A credentials. Will outlook connect internally or externally or not connect at all.

I know this is a little twisted and I also know about linked mailbox but I want to know how outlook would work in situation described by me above.

• Edited by pfgcgaurav 10 hours 58 minutes ago

What you want is known as a "resource forest".  Here's a document that will help you understand how to configure that.

https://technet.microsoft.com/en-us/library/aa998031%28v=exchg.150%29.aspx?f=255&MSPPError=-2147217396

Hi,

Thank you for your question.

When we create resource forest and account forest, then we should create DNS forward. So when we open outlook in account forest , account forest DNS will forward the request to resource forest DNS, then we could connect to Exchange server and it use the internal URL.

If there are any questions regarding this issue, please be free to let me know.

Best Regard,

Jim