i am trying to access a mailbox using EWS api.

i use a global admin with application impersonate role to access the mailbox, it failed and return an error "Unable to access an account or mailbox"

use the global admin i can access all the mailboxes but this one. I am very confused, don't know what's special about this mailbox.

I assign the global admin full access rights to this mailbox, and try to use this via powershell or EWS api to access the mailbox, it falied again.

But i can access the mailbox using its own account

Anybody know why i cannot access this mailbox using other account. I am very sure that the code i used has no problem, because it works on other mailbox.