Configuring Email Services for ASP.NET in Plesk: A Tutorial

Most ASP.NET sites need to send email: contact-form notifications, order confirmations, password resets. On Domain India Windows hosting your app sends through a mailbox you create in Plesk, over an encrypted SMTP connection. This tutorial covers the app side: which settings to use, which .NET library works with them, and how to keep the password out of your code.

1. Create a mailbox for your application

In Plesk, open Mail and click Create Email Address. A dedicated address such as [email protected] or [email protected] works well:

• it keeps app mail separate from people's inboxes;
• you can change its password without disturbing anyone;
• replies and bounces land in one place you can check.

Give it a long, random password. You will paste it into your app's configuration once, not type it again.

2. The SMTP settings your app needs

3. Why System.Net.Mail doesn't work on port 465

The classic System.Net.Mail.SmtpClient class, and the system.net/mailSettings section in web.config that feeds it, support only STARTTLS: the connection starts unencrypted and upgrades. Port 465 expects encryption from the very first byte, which SmtpClient does not support. Microsoft also recommends against SmtpClient for new development and points to MailKit instead.

So on Windows hosting, send with MailKit, a free open-source library available on NuGet:

dotnet add package MailKit

4. Sending mail with MailKit

This works in ASP.NET Core and in .NET Framework 4.x projects:

using MailKit.Net.Smtp;
using MailKit.Security;
using MimeKit;

var message = new MimeMessage();
message.From.Add(new MailboxAddress("Your Site", "[email protected]"));
message.To.Add(new MailboxAddress("", "[email protected]"));
message.Subject = "Thanks for your enquiry";
message.Body = new TextPart("plain") { Text = "We received your message." };

using var client = new SmtpClient();
await client.ConnectAsync("mail.yourdomain.com", 465, SecureSocketOptions.SslOnConnect);
await client.AuthenticateAsync("[email protected]", smtpPassword);
await client.SendAsync(message);
await client.DisconnectAsync(true);

SecureSocketOptions.SslOnConnect is the setting that matches port 465. Note that this SmtpClient is MailKit's class, not the one from System.Net.Mail.

5. Keep the password out of your code

Read the SMTP settings from configuration instead of hard-coding them.

ASP.NET Core, in appsettings.Production.json or as environment variables in web.config:

{
  "Smtp": {
    "Host": "mail.yourdomain.com",
    "Port": 465,
    "User": "[email protected]",
    "Password": "set-on-the-server-only"
  }
}

.NET Framework, in the appSettings section of web.config, read with ConfigurationManager.AppSettings.

Never commit the real password to Git. Keep a placeholder in the repository and put the real value only in the file on the server.

6. Make your mail land in the inbox

• Send from your own domain. A From address at Gmail or another provider, sent through your hosting, will fail SPF checks and be marked as spam.
• Keep the DNS records. When your domain uses the hosting nameservers, Plesk publishes MX, SPF, DKIM and DMARC records. If your DNS is elsewhere, copy them across, as described in Setting up email accounts in Plesk.
• Use Reply-To for visitor addresses. For a contact form, send from your mailbox and put the visitor's address in ReplyTo, never in From.
• Don't send bulk mail. Hosting mailboxes are for your site's own messages. Use a dedicated newsletter service for marketing lists.

7. Reading mail from your app

If your app must read a mailbox, for example to import replies, MailKit's ImapClient connects to mail.yourdomain.com on port 993 with SecureSocketOptions.SslOnConnect, using the same username and password.

8. Testing and troubleshooting

Test by sending to a mailbox you control on another provider, and check the spam folder too. More: I can receive mail but I cannot send it.

9. Where Domain India fits

Every Windows plan includes email accounts on your domain, managed in Plesk. The cards show live prices, excluding 18% GST.

If you would rather keep email separate from your hosting, Business Email is priced per mailbox.

Ready to add email to your ASP.NET app? Compare the Windows hosting plans, or open a ticket if your app still cannot send. Support is on 24/7 live chat, and tickets get a first response within 15 minutes.