Hello. There are two forests. How to delegate a mailbox from domain B, to domain A ? There is a two-way trust relationship between them.

Hi @Андрей Михалевский , Based on my research and tests, I think the Exchange server doesn't provide the function of delegating user A mailbox to user B who is from another forest. I tried the linked mailbox, cross-forest mail contact and so far there are no methods could working for our case. They all failed with "You don't have permission to open this mailbox". I find one article that's about cross forest delegation using the Outlook client to sync their calendar on Exchange 2010: Exchange Server 2010 Cross Forest Delegation And here is a similar case about Exchange Cross Forest Shared mailbox delegation , hope those could help. Best regards, Lou If the response is helpful, please click " Accept Answer " and upvote it. Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

Thank you. I get it, it's not possible.

Delegating a mailbox to another domain forest.

Accepted answer

Xzsssss 8,861 Reputation points Microsoft Vendor

2021-07-08T05:50:48.657+00:00

Hi @Андрей Михалевский ,

Based on my research and tests, I think the Exchange server doesn't provide the function of delegating user A mailbox to user B who is from another forest.
I tried the linked mailbox, cross-forest mail contact and so far there are no methods could working for our case. They all failed with "You don't have permission to open this mailbox".

I find one article that's about cross forest delegation using the Outlook client to sync their calendar on Exchange 2010: Exchange Server 2010 Cross Forest Delegation
And here is a similar case about Exchange Cross Forest Shared mailbox delegation, hope those could help.

Best regards,
Lou

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Андрей Михалевский 2,601 Reputation points

2021-07-08T05:53:37.64+00:00

Could you explain in more detail what I have to do?

Xzsssss 8,861 Reputation points Microsoft Vendor

2021-07-08T06:42:32.86+00:00

Hi @Андрей Михалевский ,

Actually if you wanna give a Full Access permission to user B, I think that's impossible, which means you couldn't open a domain A mailbox from domain B.

But for the shared mailbox, you could refer to the second link above.

If you want to GALSYNC, the steps are listed here: https://learn.microsoft.com/en-us/exchange/deploy-exchange-2013-in-a-cross-forest-topology-exchange-2013-help?redirectedfrom=MSDN#deploy-exchange-2013-in-a-cross-forest-topology-with-forefront-identity-manager-2010-r2-sp1

Best regards,
Lou

Xzsssss 8,861 Reputation points Microsoft Vendor

2021-07-08T07:10:30.787+00:00

I also tried to add the full access rights to the domain-b user, succeeded, but still, I can not open the domain-a mailbox with Open Another Mailbox on OWA.

Xzsssss 8,861 Reputation points Microsoft Vendor

2021-07-12T08:37:00.59+00:00

Hi @Андрей Михалевский ,

Do the suggestions above help? If the issue has been resolved, please click “Accept as answer” to mark the helpful reply as an answer, this will make answer searching in the forum easier and be beneficial to other community members as well.

If you are still stuck in this issue, please feel free to post your questions.

Regards,
Lou

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Delegating a mailbox to another domain forest.

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