Add .csv file extension

Rename.ps1

$folder = "C:\Users\MattSmith\OneDrive - Matt40k\Email"
$files = Get-ChildItem -Path $folder

foreach ($file in $files) {
    #Write-Host $file
    $oldName = "$folder\$file"
    $newName = "$folder\$file.csv"
    Rename-Item -Path $oldName -NewName $newName
}