VB.NET
Mailgun Send Email using MIME

Send an email using MIME. This allows for the Chilkat email object to be used to construct the email. Then it can be sent using Mailgun.
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VB.NET
Dim success As Boolean = False

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

' We're going to create an email that contains an .zip attachment,
' and also both plain-text and HTML alternative bodies.
' The HTML body will include an image.

Dim email As New Chilkat.Email

' Adding attachments, HTML/plain-text bodies, etc can be done
' in any order:

' Add an attachment
Dim contentType As String = email.AddFileAttachment("qa_data/hamlet.zip")
If (email.LastMethodSuccess = False) Then
    Debug.WriteLine(email.LastErrorText)
    Exit Sub
End If


' Add some headers:
email.Subject = "This is a complex email"
' Please change this email address before testing.
success = email.AddTo("Joe Example","joe@example.com")
email.From = "Your Name <mailgun@YOUR_DOMAIN_NAME>"

' Add a plain-text body:
email.AddPlainTextAlternativeBody("This is the plain-text body")

' Add an image that will be embedded in the HTML body.
success = email.AddRelatedFile2("qa_data/jpg/starfish.jpg","starfish.jpg")
If (success = False) Then
    Debug.WriteLine(email.LastErrorText)
    Exit Sub
End If


' Add an HTML body:
Dim html As String
html = "<html><body><b>This is the HTML body</b><br><img src=""starfish.jpg""></body></html>"

email.AddHtmlAlternativeBody(html)

' ------------------------------------------------------------------------
' Send the above email using Mailgun

Dim http As New Chilkat.Http

' Implements the following CURL command:

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

Dim req As New Chilkat.HttpRequest
req.HttpVerb = "POST"
req.Path = "/v3/YOUR_DOMAIN_NAME/messages.mime"
req.ContentType = "multipart/form-data"

req.AddParam("from","Your Name <mailgun@YOUR_DOMAIN_NAME>")
req.AddParam("to","Joe Example <joe@example.com>")
req.AddStringForUpload2("message","message.eml",email.GetMime(),"utf-8","application/octet-stream")

Dim resp As New Chilkat.HttpResponse
success = http.HttpSReq("api.mailgun.net",443,True,req,resp)
If (success = False) Then
    Debug.WriteLine(http.LastErrorText)
    Exit Sub
End If


Dim sbResponseBody As New Chilkat.StringBuilder
resp.GetBodySb(sbResponseBody)
Dim jResp As New Chilkat.JsonObject
jResp.LoadSb(sbResponseBody)
jResp.EmitCompact = False

Debug.WriteLine("Response Body:")
Debug.WriteLine(jResp.Emit())

Dim respStatusCode As Integer = resp.StatusCode
Debug.WriteLine("Response Status Code = " & respStatusCode)
If (respStatusCode >= 400) Then
    Debug.WriteLine("Response Header:")
    Debug.WriteLine(resp.Header)
    Debug.WriteLine("Failed.")
    Exit Sub
End If


' 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

Dim id As String = jResp.StringOf("id")
Dim message As String = jResp.StringOf("message")