Exchange 2013 – Grant SendOnBehalf permission for Mailbox overwrites Existing permissions

Changing **Send On Behalf **setting in Exchange 2010 / Exchange 2013 or Exchange 2016 is quite simple task that can be easily done from GUI. It gets a bit more complicated when you try to add/change **Send On Behalf **rights from PowerShell.

❗ Problem Description

Usually most people will go for

Set-Mailbox  -GrantSendOnBehalf

It's a simple command but it actually does a very dangerous thing… it overwrites current GrantSendOnBehalf permissions. While it's not a problem when it's first time you set it up, it's a big deal when there are already multiple people added to GrantSendOnBehalf field.

📧 Solution

Fortunately there's a simple way to do this to not overwrite this setting. Below you can find couple of commands that should make your life simpler.

function Add-DistributionListGrantSendOnBehalfTo { Param($newTrustee, $targetDistributionGroup)
    Set-DistributionGroup $targetDistributionGroup -GrantSendOnBehalfTo @{add=$newTrustee}
}
function Remove-DistributionListGrantSendOnBehalfTo { Param($oldTrustee, $targetDistributionGroup)
    Set-DistributionGroup $targetDistributionGroup -GrantSendOnBehalfTo @{remove=$oldTrustee}
}
function Replace-DistributionListGrantSendOnBehalfTo { Param($oldTrustee, $newTrustee, $targetDistributionGroup)
    Set-DistributionGroup $targetDistributionGroup -GrantSendOnBehalfTo @{add=$newTrustee}
    Set-DistributionGroup $targetDistributionGroup -GrantSendOnBehalfTo @{remove=$oldTrustee}
}
function Remove-MailboxGrantSendOnBehalfTo { Param($oldTrustee, $targetMailbox)
    Set-Mailbox $targetMailbox -GrantSendOnBehalfTo @{remove=$oldTrustee}
}
function Add-MailboxGrantSendOnBehalfTo { Param($newTrustee, $targetMailbox)
    Set-Mailbox $targetMailbox -GrantSendOnBehalfTo @{add=$newTrustee}
}
function Replace-MailboxGrantSendOnBehalfTo { Param($oldTrustee, $newTrustee, $targetMailbox)
    Set-Mailbox $targetMailbox -GrantSendOnBehalfTo @{remove=$oldTrustee}
    Set-Mailbox $targetMailbox -GrantSendOnBehalfTo @{add=$newTrustee}
}

**Simple usage **of Exchange PowerShell commands from above:

Add-MailboxGrantSendOnBehalfTo -NewTrustee  -TargetMailbox

Replace-MailboxGrantSendOnBehalfTo -NewTrustee  -OldTrustee  -TargetMailbox

Remove-MailboxGrantSendOnBehalfTo -OldTrustee  -TargetMailbox