# get-dllastused
# This script retrieves all distribution groups and checks the last email received for each group in the past 90 days.
# Special handling of 10 day limit and throttling  100 query requests are accepted within a 5 minute running window = 20/Minute = 1 every 3 seconds.  
# To avoid throttling, the script will wait 1 second between each query and will check the time since the last query to ensure it does not exceed the limit.

param (
    [string]$csvfilename = "DistributionGroupsLastUsed.csv"
)

Write-Host "get-dllastused: Start"
Write-Host "Retrieving distribution groups and their last email received in the past $Days days..."
Write-Host "May take some time depending on the number of groups and email traffic."
$groups = Get-DistributionGroup -ResultSize unlimited
Write-Host "Total groups retrieved: $($groups.Count)"

Write-Host "Processing groups..." -ForegroundColor Green
$count = 0
$lastcall = get-date
foreach ($group in $groups) {
    $count++
    Write-Host "Group($count/$($groups.Count)): $($group.DisplayName) ($($group.PrimarySmtpAddress))  Days back" -NoNewline

    ForEach ($intervall in 1..9) { 
        Write-Host  " $($intervall*10)" -nonewline
    
        # Throttling to prevent blocked
        $delay = [math]::Max(0, (3-((get-date) - $lastcall).TotalSeconds))
        if ($delay -gt 0) {
            Write-Host "T$($delay)Sec " -ForegroundColor Yellow -NoNewline
            Start-Sleep -Seconds $delay
        }
        #Start-Sleep -Seconds [math]::Max(0, (3-((get-date) - $lastcall).TotalSeconds))
        $lastcall = get-date    
        
        $lastMail = Get-MessageTraceV2 `
            -RecipientAddress $group.PrimarySmtpAddress `
            -StartDate (Get-Date).AddDays(-($intervall*10)) `
            -EndDate (Get-Date).AddDays(-($intervall*10 - 10)) `
        | Sort-Object Received -Descending `
        | Select-Object -First 1

        if ($lastMail) {
            Write-Host " Found: $($lastMail.Received)" -ForegroundColor Green
            break
        } 
    }
    Write-Host "lastMail: $($lastMail.Received)"

    $result = [PSCustomObject]@{
        GroupName   = $group.DisplayName
        Email       = $group.PrimarySmtpAddress
        LastMail    = $lastMail.Received
        LastSender  = $lastMail.SenderAddress
        LastSubject = $lastMail.Subject
    }
    if ($csvfilename) {
        $result | Export-Csv -Path $csvfilename -Append -NoTypeInformation
    }
    else {
        $result
    }
}

Write-Host "get-dllastused: End"