PowerShell: Exports all shared mailboxes with permissions in Microsoft 365

This script that will connect to Microsoft 365, retrieve all shared mailboxes, and list the users who have permissions on each mailbox. The results will be exported to a CSV file.

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# Install ExchangeOnlineManagement module if not already installed
if (-not (Get-Module -ListAvailable -Name ExchangeOnlineManagement)) {
    Install-Module ExchangeOnlineManagement -Force -Scope CurrentUser
}

# Import the module
Import-Module ExchangeOnlineManagement

# Connect to Exchange Online (prompt for credentials)
Connect-ExchangeOnline -UserPrincipalName admin@yourdomain.com

# Output file path
$outputFile = "C:\temp\SharedMailboxPermissions.csv"

# Retrieve all shared mailboxes
$sharedMailboxes = Get-Mailbox -RecipientTypeDetails SharedMailbox -ResultSize Unlimited

# Initialize an array to store the results
$results = @()

# Loop through each shared mailbox
foreach ($mailbox in $sharedMailboxes) {
    $permissions = Get-MailboxPermission -Identity $mailbox.PrimarySmtpAddress | Where-Object {
        $_.User -notlike "NT AUTHORITY\*" -and $_.User -notlike "S-1-5-*" # Exclude system accounts
    }

foreach ($perm in $permissions) {
        $results += [PSCustomObject]@{
            Mailbox     = $mailbox.PrimarySmtpAddress
            User        = $perm.User
            AccessRights = $perm.AccessRights -join ", "
        }
    }
}

# Export results to CSV
$results | Export-Csv -Path $outputFile -NoTypeInformation

# Disconnect from Exchange Online
Disconnect-ExchangeOnline -Confirm:$false

Write-Host "Shared mailbox permissions exported to $outputFile"

Explanation:

It retrieves all shared mailboxes using Get-Mailbox -RecipientTypeDetails SharedMailbox.
It fetches permissions using Get-MailboxPermission and filters out system accounts.
The output is stored in C:\SharedMailboxPermissions.csv.

Permissions Explanation:

FullAccess – User can open and manage mailbox items.
SendAs – User can send emails as the shared mailbox.
SendOnBehalf – User can send emails on behalf of the shared mailbox.

Prerequisites:

You must be a Microsoft 365 admin or have Exchange admin privileges.
Replace admin@yourdomain.com with your admin email.

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