ModernMail

Mail submission component capable of interacting with SMTP mail servers over the internet for delivering e-mail messages:

class Program
{
    static void Main(string[] args)
    {
        using (var msg = new MailMessage())
        {
            msg.From = new MailAddress("[email protected]", "System Administrator");
            msg.To.Add(new MailAddress("[email protected]"));
            msg.CC.Add(new MailAddress("[email protected]"));

            msg.Subject = "Hello World!";
            msg.Body = "<div>Hello,</div><br><br>" +
                "<div>This is a test e-mail with a file attached.</div><br><br>" +
                "<div>Regards,</div><br><div>System Administrator</div>";
            msg.IsBodyHtml = true;

            var plain = "Hello,\n\nThis is a test e-mail with a file attached.\n\n" +
                "Regards,\nSystem Administrator";
            var alt = AlternateView.CreateAlternateViewFromString(plain, new ContentType("text/plain"));
            msg.AlternateViews.Add(alt);

            var filePath = @"...\some-folder\pretty-image.png";
            var att = new Attachment(filePath);
            msg.Attachments.Add(att);
                
            var config = new BrokerConfig { HostName = "mydomain.com" };
            using (var broker = new MailBroker(config))
            {
                var result = broker.Send(msg);
                Console.WriteLine($"Delivered Messages: {result.Count(r => r.Delivered)}");
            }
        }

        Console.ReadKey();
    }
}

For more information and implementation details take a look at my blog post:

• Mail submission under the hood

Remarks

For increased deliverability publish your signing public key in the DNS and use the built-in DKIM signing algorithm. Also don't forget to add SPF and PTR records authorizing sending hosts and IP addresses for your domain.

Licensing

This code is released under the MIT License:

Copyright (c) TCGV.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.