PowerShell
Mailgun Send Send HTML Email with Attachments and HTML Images

Sends an HTML email with images and attachments.
Chilkat PowerShell Downloads

PowerShell
Add-Type -Path "C:\chilkat\ChilkatDotNet47-x64\ChilkatDotNet47.dll"

$success = $false

# This example assumes the Chilkat API to have been previously unlocked.
# See Global Unlock Sample for sample code.

$http = New-Object Chilkat.Http

$http.Login = "api"
$http.Password = "sending_api_key"#  Replace with your actual sending API key.

$req = New-Object Chilkat.HttpRequest
$req.HttpVerb = "POST"
$req.Path = "/v3/YOUR_DOMAIN_NAME/messages"
$req.ContentType = "multipart/form-data"

# Change YOUR_DOMAIN_NAME to something like "mg.your-domain.com".
$req.AddParam("from","Your Name <mailgun@YOUR_DOMAIN_NAME>")
$req.AddParam("to","Joe Example <joe@example.com>")
$req.AddParam("subject","Hello Joe Example")
$req.AddParam("html","<html><body><b>This is the HTML body</b><br><img src=`"cid:cidStarfish.jpg`"></body></html>")

# An a attachd file
$bd = New-Object Chilkat.BinData
$success = $bd.LoadFile("qa_data/hamlet.zip")
if ($success -eq $false) {
    $("Failed to load file attachment.")
    exit
}

$req.AddBdForUpload("attachment","hamlet.zip",$bd,"application/zip")

# add an image as CID
$success = $bd.LoadFile("qa_data/jpg/starfish.jpg")
if ($success -eq $false) {
    $("Failed to load HTML image.")
    exit
}

$req.AddBdForUpload("inline","cidStarfish.jpg",$bd,"image/jpeg")

$resp = New-Object Chilkat.HttpResponse
$success = $http.HttpSReq("api.mailgun.net",443,$true,$req,$resp)
if ($success -eq $false) {
    $($http.LastErrorText)
    exit
}

$sbResponseBody = New-Object Chilkat.StringBuilder
$resp.GetBodySb($sbResponseBody)
$jResp = New-Object Chilkat.JsonObject
$jResp.LoadSb($sbResponseBody)
$jResp.EmitCompact = $false

$("Response Body:")
$($jResp.Emit())

$respStatusCode = $resp.StatusCode
$("Response Status Code = " + $respStatusCode)
if ($respStatusCode -ge 400) {
    $("Response Header:")
    $($resp.Header)
    $("Failed.")
    exit
}

# Sample JSON response:
# (Sample code for parsing the JSON response is shown below)

# {
#   "id": "<20210429234809.1.2D550E1C94D3D98F@sandbox0e542e4c577f4bbb98c8bf6b6bca727b.mailgun.org>",
#   "message": "Queued. Thank you."
# }

# Sample code for parsing the JSON response...
# Use the following online tool to generate parsing code from sample JSON:
# Generate Parsing Code from JSON

$id = $jResp.StringOf("id")
$message = $jResp.StringOf("message")