(C++) Send Email without Mail Server

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

Note: This example requires Chilkat v11.0.0 or greater.

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#include <CkMailMan.h>
#include <CkDns.h>
#include <CkJsonObject.h>
#include <CkEmail.h>

void ChilkatSample(void)
    {
    bool success = false;

    // 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    // The answer to that question is: "Yes, it's technically possible, but it's an outdated and highly unreliable method that will likely fail in the real world."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.
    CkMailMan mailman;

    const char *recipientEmailAddr = "joe@example.com";

    // Do a DNS MX lookup for the recipient's mail server.
    CkDns dns;
    CkJsonObject json;

    // 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 == false) {
        std::cout << dns.lastErrorText() << "\r\n";
        return;
    }

    const char *smtpHostname = json.stringOf("answer.mx[0].domain");
    std::cout << smtpHostname << "\r\n";

    // Set the SMTP server.
    mailman.put_SmtpHost(smtpHostname);

    // Create a new email object
    CkEmail email;

    email.put_Subject("This is a test");
    email.put_Body("This is a test");
    email.put_From("My Name <myname@mydomain.com>");
    email.AddTo("",recipientEmailAddr);

    success = mailman.SendEmail(email);
    if (success == false) {
        std::cout << mailman.lastErrorText() << "\r\n";
        return;
    }
    }