Send and Receive Emails in ASP.NET C#

You’ve got a long ASP.NET project ahead. You’re trying to wrap your head around all tasks at hand – infrastructure, business logic, admin panel, integrations. On top of that, there’s a long list of ‘could have’ type of features that the team would like to implement if time and resources allow.

One of them is adding the ability to send an email in ASP.NET C# that you’ve been postponing for a while. After all, it’s such an obvious feature that might as well be left for the very end, when almost everything is up and running. Before your project goes live, you will need to validate your email workflows anyway and probably you don’t want to stay extra hours just before the launch to do so.

While sending emails with C# is not rocket science, we strongly recommend thinking about it sooner rather than later. To make it easier to start, we’ve covered the first steps with the various code samples. Let’s start!

MailMessage

Throughout the course of this article, we’ll often be using MailMessage class. It’s a part of System.Net.Mail namespace and is used to create email messages that are then sent to an SMTP server. The delivery is then taken care of by the SmtpClient class.

For the complete set of parameters of this class, please refer to Microsoft’s documentation.

Sending emails in C# with SMTP

This one is fairly easy and quick to set up as SMTP (Simple Mail Transfer Protocol) is the most common communication standard used in email transmission. In the example below, we’ll show how to send a very simple email with the following details:

To: [e-mail]

From: [e-mail]

Title: Good morning, Elizabeth

Body: Elizabeth, Long time no talk. Would you be up for lunch in Soho on Monday? I’m paying.

In order to send such an email, we’ll use the aforementioned MailMessage class from .NET API.

// in the beginning of the file
using System.Net;
using System.Net.Mail;
MailAddress to = new MailAddress("[e-mail]");
MailAddress from = new MailAddress("[e-mail]");
MailMessage message = new MailMessage(from, to);
message.Subject = "Good morning, Elizabeth";
message.Body = "Elizabeth, Long time no talk. Would you be up for lunch in Soho on Monday? I'm paying.;";
SmtpClient client = new SmtpClient("smtp.server.address", 2525)
{
    Credentials = new NetworkCredential("smtp_username", "smtp_password"),
    EnableSsl = true
};
// code in brackets above needed if authentication required
try
{
  client.Send(message);
}
catch (SmtpException ex)
{
  Console.WriteLine(ex.ToString());
}

Once the message was configured, we connected to the SMTP server and sent it this way!

Mailtrap Email Delivery also allows you to send emails via SMTP. Just verify your domain, copy the provided SMTP settings to your app or service, and start sending to your recipients.

Sending emails with attachments

Now that we know how to send basic emails, let’s consider a very common scenario and add an attachment to our message to the Queen of England. This could be an invoice for the last royal wedding or a set of pictures we took on that fabulous weekend.

On top of MailMessage class, we’ll use Attachment class from .NET API. Make sure you add the attachment to the current working directory first.

// in the beginning of the file
using System.Net;
using System.Net.Mail;
using System.Net.Mime;
String filePath = "wedding_invoice.pdf";
Attachment data = new Attachment(filePath, MediaTypeNames.Application.Octet);
MailAddress to = new MailAddress("[e-mail]");
MailAddress from = new MailAddress("[e-mail]");
MailMessage message = new MailMessage(from, to);
message.Subject = "Regarding our meeting";
message.Body = "Elizabeth, as requested, sending you the invoice for Harry and Meghan's wedding. Any questions? Let me know.;";
message.Attachments.Add(data);
SmtpClient client = new SmtpClient("smtp.server.address", 2525)
{
    Credentials = new NetworkCredential("smtp_username", "smtp_password"),
    EnableSsl = true
};
// code in brackets above needed if authentication required
try
{
  client.Send(message);
}
catch (SmtpException ex)
{
  Console.WriteLine(ex.ToString());
}

If you need to send multiple invoices (lucky you!) or other files, simply use a loop and add the other files to the email.

Adding images inline

We’ve just covered sending emails with attachments. But what if you’re sending images but want them displayed inline rather than being attached to an email. Certainly, it will be easier to attract the Queen’s attention this way. With a bit of modification of our previous code, this can be easily achieved.

When trying to send an email with images in C#, you’re not going to use a typical <img src="" alt="" /> construction. It would add an image attachment to the email and that’s the last thing we need right now. Instead, we’ll use LinkedResource object to directly embed an image in the HTML version of our message to the Queen. We will then follow our regular approach with MailMessage class. As always, remember to upload the file first to your current working directory. If it’s missing, an email will be sent without any attachment and, really, aren’t we receiving these “oops, forgot about the attachment!” emails too often already?

// in the beginning of the file
using System.Net;
using System.Net.Mail;
using System.Net.Mime;
String messageBody = "Elizabeth, sending you a quick sneak peak of the pictures" +
  "we took at the last royal wedding. " +
  "Let me know your thoughts.";
MailAddress to = new MailAddress("[e-mail]");
MailAddress from = new MailAddress("[e-mail]");
MailMessage message = new MailMessage(from, to);
message.Subject = "Pics from the royal wedding";
message.Body = messageBody;
String imagePath = "bestpictureever.png";
LinkedResource LinkedImage = new LinkedResource(@imagePath);
LinkedImage.ContentId = "Wedding";
AlternateView htmlView = AlternateView.CreateAlternateViewFromString(
  $"{messageBody} <br> <img src=cid:Wedding>", null, "text/html"
);
htmlView.LinkedResources.Add(LinkedImage);
message.AlternateViews.Add(htmlView);
try
{
  client.Send(message);
}
catch (SmtpException ex)
{
  Console.WriteLine(ex.ToString());
}

Sending to multiple recipients

Let’s say we want to use the opportunity and remind the Queen and her grandson about unpaid invoices.

No rocket science here either. New recipients are simply added to the code, separated by a comma. As in the example below:

// in the beginning of the file
using System.Net;
using System.Net.Mail;
MailAddress to = new MailAddress("[e-mail], [e-mail]");
MailAddress from = new MailAddress("[e-mail]");
MailMessage message = new MailMessage(from, to);
message.Subject = "Good morning";
message.Body = "Elizabeth, Harry, There are a few unpaid invoices for the Royal Wedding. Let's talk this over on Monday.;";
SmtpClient client = new SmtpClient("smtp.server.address", 2525)
{
    Credentials = new NetworkCredential("smtp_username", "smtp_password"),
    EnableSsl = true
};
// code in brackets above needed if authentication required
try
{
  client.Send(message);
}
catch (SmtpException ex)
{
  Console.WriteLine(ex.ToString());
}

Things get a tiny bit more tricky when you want to add people in bcc and cc, we’ll need a few additional lines:

// in the beginning of the file
using System.Net;
using System.Net.Mail;
MailAddress to = new MailAddress("[e-mail], [e-mail]");
MailAddress from = new MailAddress("[e-mail]");
MailMessage message = new MailMessage(from, to);
message.Subject = "Good morning";
message.Body = "Elizabeth, Harry, There are a few unpaid invoices for the Royal Wedding. Let's talk this over on Monday.;";
message.CC.Add(new MailAddress("[e-mail]"));
message.Bcc.Add(new MailAddress("[e-mail]"));
SmtpClient client = new SmtpClient("smtp.server.address", 2525)
{
    Credentials = new NetworkCredential("smtp_username", "smtp_password"),
    EnableSsl = true
};
// code in brackets above needed if authentication required
try
{
  client.Send(message);
}
catch (SmtpException ex)
{
  Console.WriteLine(ex.ToString());
}

Voila!

Do I need to have an SMTP server?

Let’s consider a situation when you don’t have (or don’t want to have) an SMTP server configured but still want to send an email in C#.

The first option is to do a DNS MX lookup of the email address that you’re trying to send an email to. This allows you to figure out what the SMTP server is and connect to it. So, you’re still going to use an SMTP server, just not yours!

We don’t, however, recommend such an approach for several reasons:

• Your emails might be treated as spam, especially if you send them from a Dynamic IP
• Each recipient’s mail server will need to be resolved manually.
• Compared to other methods, querying DNS manually consumes more CPU and networking, making the performance worse

In order to implement it, you’ll need to install a 3rd party plugin. DnsPlugin.NET is our choice here. See the sample code:

// in the top of the file
// requires installation of https://www.nuget.org/packages/DnsClient
using System.Net;
using System.Net.Mail;
using DnsClient;
MailAddress to = new MailAddress("[e-mail]");
MailAddress from = new MailAddress("[e-mail]");
MailMessage message = new MailMessage(from, to);
message.Subject = "See you Monday?";
message.Body = "Elizabeth, I didn't hear back from you. Let me know if we're still scheduled for Monday.";
LookupClient lookup = new LookupClient();
IDnsQueryResponse response = lookup.Query("westminster.co.uk", QueryType.MX);
foreach(DnsClient.Protocol.MxRecord record in response.Answers) {
    Console.WriteLine(ObjectDumper.Dump(record.Exchange));
    SmtpClient client = new SmtpClient(record.Exchange, 25);
    try
    {
        client.Send(message);
        // if we reached this point, our email was sent and we can break the loop
        break;
    }
    catch(SmtpException ex)
    {
        Console.WriteLine(ex.ToString());
    }
}

Using API to send emails

A much better approach to sending emails without SMTP is with API. It’s definitely the fastest one. It also provides an additional layer of security by utilizing API keys and allows you to use many 3rd party providers that give you tons of additional features such as analytics, email authentication, and others.

Mailtrap Email Delivery is one such service, and you get exemplary APIs for nine programming languages. More importantly, we provide comprehensive stats and deliverability alerts to help maintain your domain authority.

Receiving emails in C#

Finally, you might be wondering if there’s a way to receive the emails directly with the C# code. After all, the Queen might get back to us any minute now. Of course, you could easily track new emails with simple email clients, such as Gmail or Thunderbird, without a single line of code and with minimal effort. But let’s assume you need to see at least the topics of incoming emails with your code, for example, to build some integrations around that.

Receiving emails is not a part of core C# stack so you will need to utilize some 3rd party libraries for that purpose. OpenPop.NET open-source library seems to be getting the job done in this case. You can use the following code to fetch the topics of incoming mail:

var client = new POPClient();
client.Connect("pop.gmail.com", 995, true);
client.Authenticate("[e-mail]", "My_password_here");
var count = client.GetMessageCount();
Message message = client.GetMessage(count);
Console.WriteLine(message.Headers.Subject);

For the details on using OpenPop library for this or any other purposes, please refer to their documentation.

Summary

Try it out when you launch your first project but consider some more robust solutions if you plan to scale. If you need to do some email testing, the last thing you want is users receiving the test emails they were not supposed to get.

Testing out of the way, feel free to check out Mailtrap’s Email Delivery for free and ensure your transactional emails reach the right recipients.

That's all! Thanks for reading our guide on how to send HTML email using ASP.NET, which was originally published in the Mailtrap Blog by Piotr Malek.