Get-MailboxSendOnBehalf-Query

Exchange Online: Query-format list of mailbox SendOnBehalf permissions

Script

#Requires -Version 5.1

[CmdletBinding()]
Param(
    [Parameter(Mandatory = $true)]
    [string]$MailboxId
)

Process {
    try {
        $grantList = (Get-Mailbox -Identity $MailboxId -ErrorAction Stop).GrantSendOnBehalfTo
        $users = $grantList | Get-Mailbox -SortBy DisplayName -ErrorAction SilentlyContinue | Select-Object DisplayName, UserPrincipalName

        foreach ($itm in $users) {
            [PSCustomObject]@{
                Timestamp    = Get-Date -Format "yyyy-MM-dd HH:mm:ss"
                Value        = $itm.UserPrincipalName
                DisplayValue = $itm.DisplayName
            }
        }
    }
    catch { throw }
}

Customize

MailboxId string

User principal name of the mailbox