Sending An Email In C#/.NET

How do you send an email in C#/.NET? That sounds like it should be simple, after all, electronic mail existed decades before the Internet.

If you've worked with emails for any length of time, you'll soon hear about the Simple Mail Transfer Protocol (SMTP) for sending and Internet Message Access Protocol (IMAP - which replaced POP3) for receiving. That's an important distinction to take note of: sending, and receiving emails use different protocols.

System.Net.Mail

At first glance, SMTP seems relatively straightforward.

Here's how to write an email using System.Net.Mail (there's a better way though):

var smtpClient = new SmtpClient("smtp.example.com"){
    Port = 587,
    Credentials = new NetworkCredential("username", "password"),
    EnableSsl = true,
};
smtpClient.Send("[email protected]", "[email protected]", "subject", "body");

That doesn't actually look that bad, and might be all you need at the moment.

You can even re-write it to make an email object called MailMessage first:

var mailMessage = new MailMessage{
    From = new MailAddress("[email protected]"),
    To = new MailAddress("[email protected]"),
    Subject = "subject",
    Body = "<p>Hello</p>",
    IsBodyHtml = true,
};
smtpClient.Send(mailMessage);

You can also move the client definition to a separate appsettings.json file like so (if adding it manually then make sure to set Properties -> Copy to Output Directory -> Copy if newer):

{
  "EmailSender": {
    "SmtpHost": "smtp.gmail.com",
    "SmtpPort": 587,
    "SmtpCredential": {
      "UserName": "[email protected]",
      "Password": "App1icati0nP455w0rd"
    },
    "ProtocolLog": "Logs\\SmtpClient.txt"
  }
}

You could read those settings with Microsoft.Extensions.Configuration.Json and use them as follows (keep reading though, there's a better way!):

using Microsoft.Extensions.Configuration;

var configuration = new ConfigurationBuilder().AddJsonFile("appsettings.json").Build();
var smtpClient = new SmtpClient(configuration["EmailSender:SmtpHost"]){
    Port = int.Parse(configuration["EmailSender:SmtpPort"]),
    Credentials = new NetworkCredential(configuration["EmailSender:SmtpCredential:UserName"], configuration["EmailSender:SmtpCredential:Password"]),
    EnableSsl = true,
};

Let's simplify that by parsing the configuration to a predefined object type (later we'll re-use MailKitSimplified.Sender.Models.EmailSenderOptions):

using Microsoft.Extensions.Configuration;
var configuration = new ConfigurationBuilder().AddJsonFile("appsettings.json").Build();
var emailSenderOptions = configuration.GetRequiredSection(EmailSenderOptions.SectionName).Get<EmailSenderOptions>();
var smtpClient = new SmtpClient(emailSenderOptions.SmtpHost){
    Port = emailSenderOptions.SmtpPort,
    Credentials = emailSenderOptions.SmtpCredential,
    EnableSsl = emailSenderOptions.SmtpPort == 587 ? true : false,
};