Windows Form project, sending e-mail error in C#

Question

Windows Form project, sending e-mail error in C#

Gennady Gurin 166

Hi, I tried several things sending email pragmatically, but get an error:

enter image description here

code here:

using System.Net;

using System.Net.Mail;

private void SendEmailOutlook(string toAddress, string fromAddress, string subject, string messageText, bool isHtmlMessage, string username, string password)

{

MailAddress from = new MailAddress(fromAddress);

using (SmtpClient client = new SmtpClient("smtp.gmail.com",465) { DeliveryMethod = SmtpDeliveryMethod.Network, EnableSsl = true, UseDefaultCredentials = false })

{

    client.Credentials = new System.Net.NetworkCredential(username, password);

    MailAddress to = new MailAddress(toAddress);

    using (MailMessage message = new MailMessage(from, to) { IsBodyHtml = isHtmlMessage })

    {

        message.Subject = subject;

        message.Body = messageText;

        try { client.Send(message); } catch (Exception ex) { MessageBox.Show(ex.ToString()); }

    }

}

}

and then I call it:

SendEmailOutlook(target-email,"******@gmail.com", "subject text", " message text", false, "my-email-gmail.com", "My-Password");

Anyone can help me to figure this out.

Thanks.

Accepted answer

2 additional answers

Your answer

Answer 1

Castorix31 90,521

I had done a test app in WinUI 3 C# to test various methods to send mails : https://github.com/castorix/WinUI3_SendMail/tree/master

(same code as in WinForms, except for GUI)

I just re-tested with a gmail account and it worked with Net.Mail method, but by using an App Password (https://myaccount.google.com/apppasswords) instead of account password and 587 port

Gennady Gurin 166 Reputation points

2025-06-25T14:25:22.5466667+00:00

Should I create an app password and use net mail? And to athecate use that app password? What about username, what should that be for gmail.com account, full email account?
Castorix31 90,521 Reputation points

2025-06-25T16:13:28.9366667+00:00

Yes, but they change too often their security options (before, I needed a 2 steps verification with a "Google App Password")

I hope they won't change this for years now...

Answer 2

mudinaman143 0

✅ Solution:

Ensure your SMTP client is configured correctly:


   using System.Net.Mail;

   var client = new SmtpClient("smtp.yourserver.com");

   client.Port = 587; // Or 25/465 depending on your server

   client.Credentials = new NetworkCredential("username", "password");

   client.EnableSsl = true;

mudinaman143 0

✅ Solution:

Ensure your SMTP client is configured correctly:


   using System.Net.Mail;

   var client = new SmtpClient("smtp.yourserver.com");

   client.Port = 587; // Or 25/465 depending on your server

   client.Credentials = new NetworkCredential("username", "password");

   client.EnableSsl = true;

Answer 3

Bruce (SqlWork.com) 77,686 Volunteer Moderator

It appears you may be trying to use office 365 to send mail. The SmtpClient does not support modern authentication required office or google mail. You will need to pick a different email library.

Gennady Gurin 166 Reputation points

2025-06-25T05:22:34.7233333+00:00
I tried this method instead:

using MailKit.Net.Smtp;

using MailKit.Search;

using MimeKit;

var email = new MimeMessage();

email.From.Add(new MailboxAddress("My Name.", "******@email.com"));

email.To.Add(new MailboxAddress("Target Name", "Target@Email"));

email.Subject = "subject text";

email.Body = new TextPart(MimeKit.Text.TextFormat.Html)

{

Text = "Body Text"

};

using (var smtp = new SmtpClient())

{

smtp.Connect("smtp.gmail.com", 465, true); // Note: only needed if the SMTP server requires authentication smtp.Authenticate("******@gmail.com", "password*"); try { smtp.Send(email); MessageBox.Show("Provided email sent."); } catch (Exception ex) { MessageBox.Show(ex.ToString()); } smtp.Disconnect(true);

}

It does not even display Message Box message and does not display exception error as well.

What should I change, let me know thanks.
Bruce (SqlWork.com) 77,686 Reputation points Volunteer Moderator

2025-06-25T15:44:54.9166667+00:00

you used basic authentication (user/password) with mail kit. you need to switch to oauth. in auth you get a access token and pass to mail kit. there are two types of tokens, user and application (client, secret). generally you want to use an application token.

to use the client and secret, you need to config. for office 365, you need the azure admin to create one. for gmail, they have an admin page:

https://support.google.com/googleapi/answer/6158849?hl=en

mailkit snippet with google clientid:

https://gist.github.com/gscales/57216f70aef4b79ff2c0a0053152d5d0
Gennady Gurin 166 Reputation points

2025-06-25T16:05:18.7066667+00:00

I had to create an app password in my Gmail account instead of a regular password for login and use port 587, using net mail,

it worked, it sent successfully, who would have thought of that?
Gennady Gurin 166 Reputation points

2025-06-25T16:06:45.7833333+00:00

https://myaccount.google.com/apppasswords

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Windows Form project, sending e-mail error in C#

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