Exchange Online to introduce External Recipient Rate Limit

BoBeB good Spot have added a filter to fix this  Where-Object { $_.RecipientAddress -notlike "*@$($mailbox.PrimarySmtpAddress.Split('@')[1])" }

#Connect EXOL
Connect-ExchangeOnline

# Define the threshold for unique recipients
$threshold = 2000

# Get the current date and time
$now = Get-Date

# Calculate the start and end date for the 24-hour period
$startDate = $now.AddDays(-1)
$endDate = $now

# Get all mailboxes
$mailboxes = Get-Mailbox -ResultSize Unlimited

# Iterate through each mailbox
foreach ($mailbox in $mailboxes) {
    # Get the externally sent messages for the specified period
    $sentMessages = Get-MessageTrace -SenderAddress $mailbox.PrimarySmtpAddress -StartDate $startDate -EndDate $endDate | Where-Object { $_.RecipientAddress -notlike "*@$($mailbox.PrimarySmtpAddress.Split('@')[1])" }

    # Count the unique recipients
    $uniqueRecipients = $sentMessages.RecipientAddress | Select-Object -Unique

    # Check if the number of unique recipients exceeds the threshold
    if ($uniqueRecipients.Count -gt $threshold) {
        Write-Host "Mailbox $($mailbox.PrimarySmtpAddress) has sent to $($uniqueRecipients.Count) unique recipients in the last 24 hours."
    }
}