Hi @Mohammad Haque ,
According to my research, we cannot directly obtain the permissions of the user's mailbox to other mailboxes.We can know whether each user mailbox contains the "Full Access", "Send As" and "Send on Behalf" permissions of other mailboxes through the permissions assigned to other users on each user's mailbox.
We could run the following script to get the permission between user mailbox:
Full Access:
$mailboxes = Get-Mailbox -ResultSize Unlimited -Filter ('RecipientTypeDetails -eq "UserMailbox"')
foreach ($mailbox in $mailboxes)
{ Get-MailboxPermission -Identity $mailbox.alias -ResultSize Unlimited | ?{($_.IsInherited -eq $false) -and ($_.User -ne "NT AUTHORITY\SELF") -and ($_.AccessRights -like "FullAccess")} | select Identity, User, AccessRights }
Send As:
$mailboxes = Get-Mailbox -ResultSize Unlimited -Filter ('RecipientTypeDetails -eq "UserMailbox"')
foreach ($mailbox in $mailboxes)
{ Get-ADPermission -Identity $mailbox.alias | ? { $_.ExtendedRights -like "*send*" -and -not ($_.User -match "NT AUTHORITY") -and ($_.IsInherited -eq $false)} | select Identity,User,ExtendedRights }
Send On Behalf:
Get-Mailbox -ResultSize Unlimited -Filter ('RecipientTypeDetails -eq "UserMailbox"') | select Alias, GrantSendOnBehalfTo
The following screenshots in the test in lab environment:
Full Access:
Send As:
Send On Behalf:
----------
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.