CSharp send SMTP email with attachments.

How can we send emails in C#?

CSharp provide simple and effective SMTP mail sending clients under the System.Net.Mail namespace. We can use this with MailSlurp SMTP inboxes to send emails in .NET applications.

Install NuGet packages

To create fake email accounts for testing we can use the free MailSlurp NuGet package:

dotnet add package mailslurp
dotnet restore

Code example

using System;
using System.Net;
using System.Net.Mail;
using mailslurp.Api;
using mailslurp.Client;
using mailslurp.Model;
using Xunit;

namespace SmtpService.Tests
{
    public class UnitTest1
    {
        [Fact]
        public void CanSendEmailWithMailSlurpSmtp()
        {
            var apiKey = Environment.GetEnvironmentVariable("API_KEY")
                         ?? throw new ArgumentNullException("Missing API_KEY environment variable containing MailSlurp key");

            // configure client
            var config = new Configuration();
            config.ApiKey.Add("x-api-key", apiKey);
            var inboxController = new InboxControllerApi(config);

            // create an smtp inbox
            var inbox = inboxController.CreateInboxWithOptions(new CreateInboxDto(
                inboxType: CreateInboxDto.InboxTypeEnum.SMTPINBOX
            ));
            Assert.Contains("@mailslurp.mx", inbox.EmailAddress);

            // get smtp host, port, password, username etc
            var imapSmtpAccessDetails = inboxController.GetImapSmtpAccess();
            var smtpClient = new SmtpClient(imapSmtpAccessDetails.SmtpServerHost)
            {
                Port = imapSmtpAccessDetails.SmtpServerPort,
                Credentials = new NetworkCredential(userName: imapSmtpAccessDetails.SmtpUsername, password: imapSmtpAccessDetails.SmtpPassword),
                // disable ssl recommended
                EnableSsl = false
            };
            
            // send email to inbox
            smtpClient.Send(from: "test@external.com", recipients: inbox.EmailAddress, subject: "This inbound", body: "Hello");
            
            // wait for email to arrive
            var waitController = new WaitForControllerApi(config);
            waitController.WaitForLatestEmail(inboxId: inbox.Id, timeout: 30_000);
        }
    }
}

Next steps

Please see the CSharp documentation for more information on setting up .NET and Csharp projects to use MailSlurp SMTP inboxes.