Download files from set of folders on FTP/SFTP server with WinSCP .NET assembly in PowerShell and email results

I have this PowerShell script that I'm working on. CSV file is imported to get source and destination paths. The goal is to move files from a SFTP/FTP server into a destination and send an email report.

Task scheduler will run this code every hour. And if there's a new file, as email will be sent out.

It's almost done, but two things are missing:

Check if the file already exists and Body email seems empty: Getting the following error: Cannot validate argument on parameter 'Body'. The argument is null or empty. Provide an argument that is not null or empty, and then try the command again.
I would like some assistance on how to check if the file exists and how to get this email if a new file was dropped and copied to the destination list

$SMTPBody = ""

$SMTPMessage  = @{
  "SMTPServer" = ""
  "From" = ""
  "To" = ""
  "Subject" = "New File"
}
try {
  # Load WinSCP .NET assembly
  Add-Type -Path "C:\Program Files (x86)\WinSCP\WinSCPnet.dll"

  # Setup session options
  $sessionOptions = New-Object WinSCP.SessionOptions -Property @{
    Protocol = [WinSCP.Protocol]::sftp
    HostName = ""
    UserName = ""
    Password = ""
    PortNumber = "22"
    FTPMode = ""
    GiveUpSecurityAndAcceptAnySshHostKey = $true
  }
  $session = New-Object WinSCP.Session
  try
  {
    # Connect
    $session.Open($sessionOptions)
    # Download files
    $transferOptions = New-Object WinSCP.TransferOptions
    $transferOptions.TransferMode = [WinSCP.TransferMode]::Binary

    Import-Csv -Path "D:\FILESOURCE.csv" -ErrorAction Stop |  foreach {

      $synchronizationResult = $session.SynchronizeDirectories(
        [WinSCP.SynchronizationMode]::Local, $_.Destination, $_.Source, $False)
      $synchronizationResult.Check()

      foreach ($download in $synchronizationResult.Downloads ) {
        Write-Host "File $($download.FileName) downloaded" -ForegroundColor Green
        $SMTPBody +=
          "`n Files: $($download.FileName -join ',    ') `n" +
          "Current Location: $($_.Destination)`n"
        Send-MailMessage @SMTPMessage  -Body $SMTPBody
      }

      $transferResult =
        $session.GetFiles($_.Source, $_.Destination, $False, $transferOptions)
      #Find the latest downloaded file
      $latestTransfer =
        $transferResult.Transfers |
        Sort-Object -Property @{ Expression = { (Get-Item $_.Destination).LastWriteTime }
        } -Descending |Select-Object -First 1
    }

    if ($latestTransfer -eq $Null) {
      Write-Host "No files found."
      $SMTPBody += "There are no new files at the moment"
    }
    else
    {
      $lastTimestamp = (Get-Item $latestTransfer.Destination).LastWriteTime
      Write-Host (
        "Downloaded $($transferResult.Transfers.Count) files, " +
        "latest being $($latestTransfer.FileName) with timestamp $lastTimestamp.")
      $SMTPBody += "file : $($latestTransfer)"
    }

    Write-Host "Waiting..."
    Start-Sleep -Seconds 5
  }  
  finally
  {
    Send-MailMessage @SMTPMessage  -Body  $SMTPBody
    # Disconnect, clean up
    $session.Dispose()
  }
}
catch
{
  Write-Host "Error: $($_.Exception.Message)"
}

Solution

I believe your code has more problems than you think.

Your combination of SynchronizeDirectories and GetFiles is suspicious. You first download only the new files by SynchronizeDirectories and then you download all files by GetFiles. I do not think you want that.
On any error the .Check call will throw and you will not collect the error into your report.
You keep sending partial reports by Send-MailMessage in the foreach loop

This is my take on your problem, hoping I've understood correctly what you want to implement:

$SMTPBody = ""

Import-Csv -Path "FILESOURCE.csv" -ErrorAction Stop |  foreach {

    Write-Host "$($_.Source) => $($_.Destination)"
    $SMTPBody += "$($_.Source) => $($_.Destination)`n"

    $synchronizationResult =
        $session.SynchronizeDirectories(
            [WinSCP.SynchronizationMode]::Local, $_.Destination, $_.Source, $False)

    $downloaded = @()
    $failed = @()
    $latestName = $Null
    $latest = $Null
    foreach ($download in $synchronizationResult.Downloads)
    {
        if ($download.Error -eq $Null)
        {
            Write-Host "File $($download.FileName) downloaded" -ForegroundColor Green
            $downloaded += $download.FileName
            $ts = (Get-Item $download.Destination).LastWriteTime
            if ($ts -gt $latest)
            {
                $latestName = $download.FileName;
                $latest = $ts
            }
        }
        else
        {
            Write-Host "File $($download.FileName) download failed" -ForegroundColor Red
            $failed += $download.FileName
        }
    }

    if ($downloaded.Count -eq 0)
    {
        $SMTPBody += "No new files were downloaded`n"
    }
    else
    {
        $SMTPBody += 
            "Downloaded $($downloaded.Count) files:`n" +
            ($downloaded -join ", ") + "`n" +
            "latest being $($latestName) with timestamp $latest.`n"
    }

    if ($failed.Count -gt 0)
    {
        $SMTPBody += 
            "Failed to download $($failed.Count) files:`n" +
            ($failed -join ", ") + "`n"
    }

    $SMTPBody += "`n"
}

It will give you a report like:

/source1 => C:\dest1`
Downloaded 3 files:
/source1/aaa.txt, /source1/bbb.txt, /source1/ccc.txt
latest being /source1/ccc.txt with timestamp 01/29/2020 07:49:07.

/source2 => C:\dest2
Downloaded 1 files:
/source2/aaa.txt
latest being /source2/aaa.txt with timestamp 01/29/2020 07:22:37.
Failed to download 1 files:
/source2/bbb.txt