Create new email in the default mail client, and optionally include an attachment.

Invoke-MailTo.ps1

function Invoke-MailTo {
param(
[OutputType([bool])]
    [Parameter(Mandatory)]
    [ValidateNotNullOrEmpty()]
    [string]$To,

    [Parameter(Mandatory)]
    [string]$Subject,
    
    [Parameter(Mandatory)]
    [string]$Body,

    [Parameter()]
    [ValidateScript({Test-Path $_})]
    $Attachment = ""
)
    if ($Attachment.FullName) {$Attachment = $Attachment.FullName}
    $MailToURL = 'mailto:{0}?subject={1}&body={2}&attach={3}' -f $To,$Subject,$Body,$Attachment
    try   { Invoke-Expression $("start '{0}'" -f $MailToURL) ; Write-Output $true }
    catch { $false }
}