Why Do I Get "'Property Cannot Be Assigned" When Sending an Smtp Email

Why do I get 'property cannot be assigned when sending an SMTP email?

mail.To and mail.From are readonly. Move them to the constructor.

using System.Net.Mail;

...

MailMessage mail = new MailMessage("you@yourcompany.example", "user@hotmail.com");
SmtpClient client = new SmtpClient();
client.Port = 25;
client.DeliveryMethod = SmtpDeliveryMethod.Network;
client.UseDefaultCredentials = false;
client.Host = "smtp.gmail.com";
mail.Subject = "this is a test email.";
mail.Body = "this is my test email body";
client.Send(mail);

Property or indexer Attachments cannot be assigned to -- it is read only

Why complicate the code like that. You need to use message.Attachments.Add since the Attachments property is read-only :

var message = new MailMessage(fromAddress, toAddress)
{
    Subject = Environment.MachineName,
    Body = "PC NAME : " + Environment.MachineName + "\r\nIP ADRESS : " + Dns.GetHostEntry(Dns.GetHostName()).AddressList[1],
};
message.Attachments.Add(new Attachment(@"c:\MyDir\Img" + "/img" + (Saving.CountImagesTaken(@"c:\MyDir\Img") - 1).ToString() + ".png"));
using (message)
{
    smtp.Send(message);
}

Send mail to user - SmtpException causes problems

I have designed a component that handles Emails

First add my class to your project.

using System.ComponentModel;
using System.Net.Mail;
using System.Net;
using System.ComponentModel.DataAnnotations;

namespace Hector.Framework.Controls
{
    public class MailMessageControl : Component
    {
        private MailMessage Mail = new MailMessage();
        private SmtpClient SmtpClient = new SmtpClient();

        public MailMessageControl()
        {
            Host = "smtp.gmail.com";
            Port = 587;
            EnableSSL = true;
        }

        public string Host
        {
            get => SmtpClient.Host;
            set => SmtpClient.Host = value;
        }

        public int Port
        {
            get => SmtpClient.Port;
            set => SmtpClient.Port = value;
        }

        public bool EnableSSL
        {
            get => SmtpClient.EnableSsl;
            set => SmtpClient.EnableSsl = value;
        }

        public void AttachFile(string path)
        {
            Mail.Attachments.Add(new Attachment(path));
        }

        public void SetCredentials(string mail, string password)
        {
            SmtpClient.Credentials = new NetworkCredential(mail, password);
        }

        public void SetSender(string mail)
        {
            Mail.From = new MailAddress(mail);
        }

        public void AddAddressSee(string mail)
        {
            Mail.To.Add(mail);
        }

        public void SetSubject(string subject)
        {
            Mail.Subject = subject;
        }

        public void SetBody(string body, bool isHTML)
        {
            Mail.IsBodyHtml = isHTML;
            Mail.Body = body;
        }

        public bool SendEmail()
        {
            try
            {
                SmtpClient.Send(Mail);
                return true;
            }
            catch
            {
                return false;
            }
        }

        public bool IsValidEmail(string email)
        {
            try
            {
                return new MailAddress(email).Address == email;
            }
            catch
            {
                return false;
            }
        }

        public bool EmailIsValidated(string email)
        {
            return new EmailAddressAttribute().IsValid(email);
        }
    }
}

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Usage example:

Hector.Framework.Controls.MailMessageControl mail = new Hector.Framework.Controls.MailMessageControl();
mail.SetCredentials("Your gmail email", "Your gmail password");
mail.SetSender("Sender mail");
mail.AttachFile("Your file path"); //If you want send file
mail.AddAddressSee("Add mail to receive your message");
mail.SetSubject("Subject");
mail.SetBody("Body", false);

if(mail.SendEmail())
{
  //Mail send correctly
}
else
{
  //Error
}

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Now go to the following link: https://myaccount.google.com/lesssecureapps

And enable this switch:

This allows your program to use your credentials to send emails, if you do not activate it, it may result in an error.

After activating it, try to send a message

Sending E-mail for SMTP error

MailMessage.To is a read-only property. It returns a list of MailAdresses you added to the message.

To add a MailAddress, you should use:

mm.To.Add(new MailAddress(txtTo.Text, txtReceiver.Text));

System.ObjectDisposedException while sending email using smtpclient (fluent-email)

The extensions provided by fluent-email did inject these classes as singleton and I did use another lifetime and therefore this issue occured.

So I forgot to also override the dependency injection container configuration for all dependencies using the System.ObjectDisposedException to use singleton, since I was using a custom implementation of FluentEmail.Smtp.SendMailEx.SendMailExImplAsync.

After overridding the other dependencies in the DI extension, it worked.

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