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This example demonstrates how to send emails in ASP.NET Core using the SmtpClient with configuration from appsettings.json.

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Overview

The email sending feature allows your application to send HTML emails using SMTP. Configuration is externalized to settings files for easy environment-specific changes.

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Complete Implementation

1

Configure Email Settings

Add email configuration to your appsettings.json or appsettings.Development.json.
appsettings.json
{
  "MailSettings": {
    "Credentials": {
      "User": "[email protected]",
      "Password": "your-app-password"
    }
  },
  "Server": {
    "Host": "smtp.gmail.com",
    "Port": 587,
    "Ssl": true,
    "DefaultCredentials": false
  }
}
Never commit real credentials to source control. Use:
  • User Secrets for development
  • Environment variables for production
  • Azure Key Vault or similar for sensitive data

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Common SMTP Providers

ProviderHostPortSSL
Gmailsmtp.gmail.com587true
Outlooksmtp-mail.outlook.com587true
Office 365smtp.office365.com587true
SendGridsmtp.sendgrid.net587true
2

Create the Mail Controller

The controller reads SMTP settings from configuration and sends emails.
Controllers/MailsController.cs
using Microsoft.AspNetCore.Mvc;
using System.Net;
using System.Net.Mail;

namespace MvcCoreUtilidades.Controllers
{
    public class MailsController : Controller
    {
        private IConfiguration configuration;

        public MailsController(IConfiguration configuration)
        {
            this.configuration = configuration;
        }

        public IActionResult SendMail()
        {
            return View();
        }

        [HttpPost]
        public async Task<IActionResult> SendMail(string to, string asunto, string mensaje)
        {
            string user = this.configuration.GetValue<string>("MailSettings:Credentials:User");
            MailMessage mail = new MailMessage();
            mail.From = new MailAddress(user);
            mail.To.Add(to);
            mail.Subject = asunto;
            mail.Body = mensaje;
            mail.IsBodyHtml = true;
            mail.Priority = MailPriority.Normal;
            string password = this.configuration.GetValue<string>("MailSettings:Credentials:Password");
            string host = this.configuration.GetValue<string>("Server:Host");
            int port = this.configuration.GetValue<int>("Server:Port");
            bool ssl = this.configuration.GetValue<bool>("Server:Ssl");
            bool defaultCredentials = this.configuration.GetValue<bool>("Server:DefaultCredentials");
            SmtpClient client = new SmtpClient();
            client.Host = host;
            client.Port = port;
            client.EnableSsl = ssl;
            client.UseDefaultCredentials = defaultCredentials;  // Set BEFORE credentials
            NetworkCredential credentials = new NetworkCredential(user, password);
            client.Credentials = credentials;  // Set AFTER
            await client.SendMailAsync(mail);
            ViewData["MENSAJE"] = "Mensaje enviado correctamente.";
            return View();
        }
    }
}
See MailsController.cs:21
Important: Set UseDefaultCredentials = false BEFORE setting custom credentials. The order matters!
3

Create the View

The view provides a form to compose and send emails.
Views/Mails/SendMail.cshtml
<h1>Send Mail Net Core</h1>

<form method="post" class="my-2">
    <label>To: </label>
    <input type="text" name="to" class="form-control" 
    <label>Asunto: </label>
    <input type="text" name="asunto" class="form-control" />
    <label>Mensaje: </label>
    <textarea name="mensaje" class="form-control"></textarea>
    <button class="btn btn-info my-2">Send mail</button>
</form>

<h2 style="color:blue">@ViewData["MENSAJE"]</h2>
4

Inject Configuration Service

The IConfiguration service is automatically available via dependency injection.
public MailsController(IConfiguration configuration)
{
    this.configuration = configuration;
}
No additional service registration needed - configuration is built-in to ASP.NET Core.

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How It Works

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Email Sending Workflow

MailMessage mail = new MailMessage();
mail.From = new MailAddress(user);
mail.To.Add(to);
mail.Subject = asunto;
mail.Body = mensaje;
mail.IsBodyHtml = true;
mail.Priority = MailPriority.Normal;

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Reading Configuration

// Read string value
string user = this.configuration.GetValue<string>("MailSettings:Credentials:User");

// Read int value
int port = this.configuration.GetValue<int>("Server:Port");

// Read bool value
bool ssl = this.configuration.GetValue<bool>("Server:Ssl");

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Usage Example

  1. Navigate to /Mails/SendMail
  2. Enter recipient email address in “To” field
  3. Enter subject in “Asunto” field
  4. Enter message body (supports HTML) in “Mensaje” field
  5. Click “Send mail”
  6. Success message displays when sent

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Gmail Configuration

For Gmail accounts, you need to use an App Password instead of your regular password.
1

Enable 2-Factor Authentication

Go to your Google Account settings and enable 2-Step Verification.
2

Generate App Password

  1. Go to Google App Passwords
  2. Select “Mail” and “Other (Custom name)”
  3. Copy the 16-character password
3

Update Configuration

{
  "MailSettings": {
    "Credentials": {
      "User": "[email protected]",
      "Password": "your-16-char-app-password"
    }
  },
  "Server": {
    "Host": "smtp.gmail.com",
    "Port": 587,
    "Ssl": true,
    "DefaultCredentials": false
  }
}

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Advanced Features

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Sending HTML Emails

mail.Body = @"
<html>
  <body>
    <h1>Welcome!</h1>
    <p>This is an <strong>HTML email</strong>.</p>
  </body>
</html>";
mail.IsBodyHtml = true;

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Adding Attachments

string filePath = Path.Combine("wwwroot", "documents", "report.pdf");
Attachment attachment = new Attachment(filePath);
mail.Attachments.Add(attachment);

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Multiple Recipients

// To
mail.To.Add("[email protected]");
mail.To.Add("[email protected]");

// CC
mail.CC.Add("[email protected]");

// BCC
mail.Bcc.Add("[email protected]");

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Custom Priority

mail.Priority = MailPriority.High;    // High priority (!)
mail.Priority = MailPriority.Normal;  // Normal (default)
mail.Priority = MailPriority.Low;     // Low priority

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Error Handling

The current implementation doesn’t handle errors. For production, add try-catch:
[HttpPost]
public async Task<IActionResult> SendMail(string to, string asunto, string mensaje)
{
    try
    {
        // ... email sending code ...
        await client.SendMailAsync(mail);
        ViewData["MENSAJE"] = "Mensaje enviado correctamente.";
    }
    catch (SmtpException ex)
    {
        ViewData["MENSAJE"] = $"Error SMTP: {ex.Message}";
    }
    catch (Exception ex)
    {
        ViewData["MENSAJE"] = $"Error: {ex.Message}";
    }
    return View();
}

​
Common Issues

Causes:
  • Wrong username/password
  • Gmail: Not using App Password
  • 2FA not enabled (Gmail)
Solution:
  • Verify credentials in appsettings.json
  • Generate and use App Password for Gmail
Causes:
  • Wrong host or port
  • SSL setting mismatch
  • Firewall blocking SMTP
Solution:
  • Verify host and port for your provider
  • Check SSL setting matches provider requirements
  • Test SMTP connectivity from your server
Cause:
  • Setting custom credentials before UseDefaultCredentials = false
Solution:
  • Always set UseDefaultCredentials = false FIRST
  • Then set Credentials property

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Production Recommendations

Best Practices:
  • Use dedicated email service (SendGrid, AWS SES, etc.)
  • Implement email queue for reliability
  • Add retry logic for failed sends
  • Log email sending attempts
  • Validate email addresses before sending
  • Rate limit to prevent abuse
Alternative: Consider using dedicated email libraries like:
  • MailKit (modern, cross-platform)
  • FluentEmail (fluent interface)
  • SendGrid SDK (if using SendGrid)

MailsController

Complete API reference for email controller

Email Utility

Learn more about email configuration and features

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