Using @Splat to send email attachment result and then delete after successful execution

Question

I wish to modify the script below to:

1. Attach the Result HTML file that is written to Desktop folder, then send the email.
2. Delete/clean up the HTML file after successful email sent.

The script below basically gets all the Event ID 4625 in the past 1 hour from all domain controllers.

$DCServers = Get-ADDomainController -filter * | select -ExpandProperty hostname

$events = @()
$totalCt = 0
$servers = @()

$hashLogonType = @{
    2 = "Interactive"
    3 = "Network"
    4 = "Batch (eg. Scheduled Task)"
    5 = "Service"
    7 = "Unlock (eg. Workstation Screen saver)"
    8 = "NetworkCleartext (eg. IIS Basic Auth.)"
    9 = "NewCredentials"
    10 = "Remote Desktop"
    11 = "Logon With Cached Credentials"
}

Foreach ($Server in $DCServers)
{
    Write-Host "Calling Get-WinEvent for $Server"
    $serverEvents = Get-WinEvent -ComputerName $Server -FilterHashtable @{ logname = 'Security'; id = 4625; StartTime = (Get-Date).AddHours(-1) } -EA 0
    if (!$?)
    {
        Write-Host "Get-WinEVent failure for $Server"
        continue
    }
    if ($null -ne $serverEvents)
    {
        $totalCt += $serverEvents.Count
        $servers += [PsCustomObject] @{ $server = $serverEvents.Count }
        Write-Host $server $serverEvents.Count
    }
   
    $serverEvents | ForEach-Object {
        $events += [PsCustomObject] @{
            Date = $_.TimeCreated
            "Event Id" = $_.Id
            "User Name" = $_.Properties[6].Value + "\" + $_.Properties[5].Value ## fixed
            "WorkstationName" = $_.Properties.Value[13]
            "IPAddress" = $_.Properties.Value[19]
            "FailureReason" = (($_.message -split "\n") | Select-String -Pattern "Failure Reason:\s+(.+)").matches[0].groups[1].value
            "Status Code" = $_.message -split '\s{4}' | Select-String -Pattern "Status"
            "Logon Type" = $hashLogonType.$([int]$_.Properties[10].Value)
        }
    }
}


$HTML = @"
<style>
   body {
      font-family: Arial;
   }
   table {
      width: 100%;
      border-collapse: collapse;
      border: 1px solid;
   }
   th {
      background-color: green;
      border: 1px solid;
      padding: 1px;
   }
   td {
      border: 1px solid;
      padding: 1px;
   }
</style>
"@
$GetDate = Get-Date -Format 'F'
$Report = "[Environment]::GetFolderPath("Desktop")\temp-4625.html"
Invoke-Item $Report


#convert the array of events to HTML
$Events | Select-Object Date, "User Name", "WorkstationName", "IPAddress", "Logon Type" |
Convertto-html -head $HTML -PreContent "<H2>Accounts that Failed to Log On</H2>", "<H2>$GetDate </H2>", "<br> FailureReason   = $((($_.message -split "\n") | Select-String -Pattern "Failure Reason:\s+(.+)").matches[0].groups[1].value)<br>", "<br> Status Code     = $($_.message -split '\s{4}' | Select-String -Pattern "Status")<br>"
-PostContent "<p></p>Total Event ID 4625 records: <b><u>$totalCt</u></b> <p></p>" | Out-File $Report -append


Write-Host "Total Event ID 4625 records: $totalCt"
Write-Host "Event ID 4625 records per server:"
$servers | Format-Table -autosize


Write-Host "4625 records grouped by user"
$events | Group-Object "User Name" | Sort-Object Count | Out-GridView -Title "4625 records grouped by user"


Write-Host "4625 records grouped by IP Address"
$events | Group-Object "IPAddress" | Sort-Object Count | Out-GridView -Title "4625 records grouped by IP Address"


Write-Host "4625 records grouped by WorkstationName"
$events | Group-Object "WorkstationName" | Sort-Object Count | Out-GridView -Title "4625 records grouped by WorkstationName"


$sendMailArgs = @{
    From = "$env:COMPUTERNAME@$env:userdnsdomain"
    To   = 'IT@corp.com'
    Subject = "Event ID 4625 Result as at $(Get-Date -Format 'F')"
    SmtpServer = 'smtp.domain.com'
    BodyAsHtml = $true
}
$sendMailArgs['Body'] = "<H3>Total Event ID 4625 records: $($totalCt)</H3>"

Send-MailMessage @sendMailArgs -Priority High -Verbose -Attachments $Report

However, the error is like below:

Send-MailMessage : Cannot find a provider with the name '[Environment]'.
At line:103 char:1
+ Send-MailMessage @sendMailArgs -Priority High -Verbose -Attachments $ ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : ObjectNotFound: ([Environment]:String) [Send-MailMessage], ProviderNotFoundException
    + FullyQualifiedErrorId : ProviderNotFound,Microsoft.PowerShell.Commands.SendMailMessage

and there is no email sent out. How can I debug this?