🚀 Scripting Bulk Mailbox Delegation in Exchange Online

When managing a growing team, you often find yourself in a situation where a lead user (e.g., a department head or administrator) needs access to multiple shared or functional mailboxes.

Manually clicking through the Microsoft 365 Admin Center for 10+ mailboxes is a recipe for boredom and typos. Here is how I solved this using the Exchange Online PowerShell V3 module.

The Scenario

We need to grant one primary user (User A) two specific types of permissions across a list of target mailboxes:

1. FullAccess: The ability to open the mailbox, read, and organize emails.
2. SendAs: The ability to send emails appearing as the target mailbox address.

The PowerShell Solution

First, ensure you are connected:

Connect-ExchangeOnline

Then, run this script to loop through your targets:

PowerShell

# 1. Define the Lead User (The one receiving the permissions)
$LeadUser = "primary.user@company-it.com"

# 2. Define the list of target mailboxes (Shared or User mailboxes)
$TargetMailboxes = @(
    "info@company-it.com",
    "accounting@company-it.com",
    "logistics@company-it.com",
    "project-alpha@company-it.com",
    "support@company-it.com",
    "hr-dept@company-it.com"
)

# 3. Apply permissions via loop
foreach ($Mailbox in $TargetMailboxes) {
    Write-Host "Processing: $Mailbox" -ForegroundColor Cyan

    # Grant Full Access (includes Auto-Mapping for Outlook Desktop)
    Add-MailboxPermission -Identity $Mailbox -User $LeadUser -AccessRights FullAccess -InheritanceType All -Confirm:$false

    # Grant Send As permissions
    Add-RecipientPermission -Identity $Mailbox -Trustee $LeadUser -AccessRights SendAs -Confirm:$false
}

Write-Host "Success: All permissions applied." -ForegroundColor Green