Sending Email in C# (.NET): SmtpClient and MailKit |…

Sending Email in C# (.NET): From SmtpClient to MailKit

Sending emails is one of the key tasks when developing web applications, notification services, and enterprise systems. The .NET ecosystem offers both built-in tools and third-party libraries that simplify working with SMTP, SSL/TLS, and complex scenarios. In this article, we will thoroughly examine how to send an email in C# using the classic SmtpClient and the modern MailKit library.

1. Built-in SmtpClient (System.Net.Mail)

The SmtpClient class is available in .NET Framework and .NET Core/5+ (with some limitations). It allows you to quickly configure sending an email through any SMTP server.

Basic Email Sending Example

using System.Net;using System.Net.Mail;

var smtpClient = new SmtpClient("smtp.gmail.com"){    Port = 587,    Credentials = new NetworkCredential("your_email@gmail.com", "your_app_password"),    EnableSsl = true};

var mailMessage = new MailMessage{    From = new MailAddress("your_email@gmail.com"),    Subject = "Test email from C#",    Body = "Hello! This message was sent via SmtpClient.",    IsBodyHtml = false};

mailMessage.To.Add("recipient@example.com");

try{    smtpClient.Send(mailMessage);    Console.WriteLine("Email sent successfully!");}catch (Exception ex){    Console.WriteLine($"Sending error: {ex.Message}");}

Important: For Gmail, you will need an app password, not your regular password. For other services (Yandex, Mail.ru), check their SMTP settings.

Sending an HTML Email with an Attachment

var message = new MailMessage();message.From = new MailAddress("sender@example.com");message.To.Add("user@example.com");message.Subject = "Monthly Report";message.IsBodyHtml = true;message.Body = "<h2>Monthly Report</h2><p>A PDF file is attached.</p>";

// Add an attachmentvar attachment = new Attachment(@"C:\\Reports\\report.pdf");message.Attachments.Add(attachment);

using (var client = new SmtpClient("smtp.example.com", 587)){    client.Credentials = new NetworkCredential("login", "password");    client.EnableSsl = true;    client.Send(message);}

Attachments can be of any type: images, documents, archives. To send from memory, use MemoryStream.

2. Asynchronous Sending

In modern applications, it is advisable not to block the thread. Use SendMailAsync:

public async Task SendEmailAsync(){    using var client = new SmtpClient("smtp.example.com", 587);    client.Credentials = new NetworkCredential("login", "password");    client.EnableSsl = true;

    var message = new MailMessage("from@example.com", "to@example.com")    {        Subject = "Asynchronous Sending",        Body = "This email was sent asynchronously."    };

    await client.SendMailAsync(message);    Console.WriteLine("Sent asynchronously!");}