Visual Basic 6.0

Send Email without Mail Server

How to send an email without a mail server (so-to-speak). Visual Basic 6.0

Dim success As Long
success = 0

' Sending Email: Do You Really Need an SMTP Server?
' 
' A common question developers ask is: "Can my application send email without connecting to a mail server?"
' 
' The short answer is: No, not really. Every email sent over the internet must be handed to a Simple Mail Transfer Protocol (SMTP) server.
' 
' What people usually mean is: "My application doesn't have credentials for a dedicated SMTP server. 
' Can it send an email directly to the recipient's server without me needing to configure one?"
' 
' The answer to that question is: "Yes, it's technically possible, but it's an outdated and highly unreliable method that will likely fail in the real world." 
' Let's explore how it works and, more importantly, why you shouldn't use it.
' 
' How "Serverless" Email Sending Works
' 
' Components and libraries that claim to send email without a configured server perform a clever trick behind the scenes:
' 
'     DNS MX Lookup: They take the recipient's email address (e.g., recipient@example.com) and perform a special DNS query to find the Mail Exchange (MX) records for the example.com domain.
' 
'     Direct Connection: This MX record provides the hostname of the SMTP server responsible for handling email for that domain (e.g., mx.example.com).
' 
'     Delivery Attempt: The library then connects directly to that server on the standard SMTP port (25) and attempts to deliver the email.
' 
' You're still connecting to an SMTP server�just the recipient's, not your own.
' Why This Method Fails in Modern Applications
' 
' While this process seems straightforward, it is almost guaranteed to fail for two critical reasons. These aren't minor "gotchas"; they are fundamental roadblocks in today's internet infrastructure.
' 
' Problem #1: Most Networks Block Port 25
' 
' To combat spam, nearly all residential Internet Service Providers (ISPs) like Comcast and Spectrum, corporate firewalls, and cloud providers (AWS, Azure, Google Cloud) 
' block outgoing connections on port 25 to any server except their own.
' 
' If your application is running on a user's home computer or within a typical corporate or cloud network, its attempt to connect to a random recipient's mail server 
' will be blocked before it even starts. The connection will simply time out.
' 
' Problem #2: You Have No IP Reputation
' 
' Email servers are built on trust. They will not accept mail from unknown, untrusted sources.
' 
' When your application connects directly from its IP address (especially a dynamic IP from a residential ISP), the recipient's server will see it as a suspicious, 
' unauthenticated connection. It will likely be rejected for several reasons:
' 
'     No Authentication: You are not logging in to prove who you are.
' 
'     Poor IP Reputation: The IP address has no history of sending legitimate mail.
' 
'     Blacklists (DNSBLs): The IP is likely on a DNS Blackhole List (DNSBL) that flags dynamic IPs as sources of spam.
' 
' You will receive an error message from the server, like this common example:
' 
' 553-Your message was rejected because it appears to be spam.
' 553-The IP address [your.ip.address.here] is listed on the SORBS DUHL blacklist.
' 553 To request removal, see http://www.sorbs.net/
' The Modern, Reliable Solution: Use an Authenticated Relay
' 
' Instead of trying to deliver mail directly, the correct and reliable method is to relay your email through a server that you can 
' authenticate with. This solves all the problems mentioned above.
' 
' There are two primary ways to do this:
' 
'     Authenticated SMTP Relay (The Standard)
' 
' You configure your application to connect to a dedicated mail server that knows and trusts you.
' 
'     How it Works: You connect using a specific port designed for authenticated sending (port 587 or 465), which is not blocked by firewalls. 
'     You then provide a username and password (or API key) to authenticate.
' 
'     Why it Works: You are now a trusted user on a server that has a high IP reputation. That server handles the final delivery to the recipient, who will trust mail coming from it.
' 
'     Examples: Your ISP's mail server (e.g., smtp.comcast.net), your web host's server, or your company's Microsoft 365 or Google Workspace mail server.
' 
'     Transactional Email API Services (The Professional Standard)
' 
' For applications, the best practice is to use a dedicated email delivery service.
' 
'     How it Works: Instead of dealing with SMTP directly, you use a simple API (like a REST API) to send your email. 
'     The service handles all the complexities of delivery, reputation, and compliance.
' 
'     Why it's Better: These services are built for high-volume, reliable delivery. They provide detailed analytics (opens, clicks, bounces), 
'     manage IP reputation across entire server farms, and ensure your mail doesn't land in the spam folder.
' 
'     Examples: SendGrid, Mailgun, Postmark, and Amazon SES.
' 
' Conclusion
' 
' While the idea of sending email without a configured server is tempting, the direct-to-MX method is an obsolete technique that is fundamentally incompatible 
' with the security and anti-spam measures of the modern internet.
' 
' For reliable email delivery, always use an authenticated SMTP relay or a dedicated transactional email API service.

' ----------------------------------------------------------
' The following code is NOT recommended as explained above:
' ----------------------------------------------------------

' The mailman object is used for sending and receiving email.
Dim mailman As New ChilkatMailMan

Dim recipientEmailAddr As String
recipientEmailAddr = "joe@example.com"

' Do a DNS MX lookup for the recipient's mail server.
Dim dns As New ChilkatDns
Dim json As New ChilkatJsonObject

' This gets all MX domains for an email address.  (Typically one domain.)
' The preferred domain will be at index 0 (see below).
success = dns.Query("MX",recipientEmailAddr,json)
If (success = 0) Then
    Debug.Print dns.LastErrorText
    Exit Sub
End If

Dim smtpHostname As String
smtpHostname = json.StringOf("answer.mx[0].domain")
Debug.Print smtpHostname

' Set the SMTP server.
mailman.SmtpHost = smtpHostname

' Create a new email object
Dim email As New ChilkatEmail

email.Subject = "This is a test"
email.Body = "This is a test"
email.From = "My Name <myname@mydomain.com>"
success = email.AddTo("",recipientEmailAddr)

success = mailman.SendEmail(email)
If (success = 0) Then
    Debug.Print mailman.LastErrorText
    Exit Sub
End If