Why Do I Get an Error When Assigning to `MailMessage.To` and `MailMessage.From`?

Troubleshooting Read-Only Properties in MailMessage for SMTP Email Sending

The Issue:

Sending emails via SMTP often involves using the MailMessage and SmtpClient classes. A common error arises when attempting to directly assign values to the To and From properties of MailMessage. These properties are read-only, leading to an assignment error.

The Incorrect Approach (and why it fails):

The following code snippet demonstrates the flawed approach:

<code class="language-csharp">MailMessage mail = new MailMessage();
mail.To = "[email protected]"; // Error! To is read-only.
mail.From = "[email protected]"; // Error! From is read-only.
// ... rest of the email sending code ...</code>

The error occurs because MailMessage.To and MailMessage.From are not designed for direct assignment after object creation.

The Solution:

The correct way to set the recipient and sender addresses is to pass them directly into the MailMessage constructor:

<code class="language-csharp">MailMessage mail = new MailMessage("[email protected]", "[email protected]");
// ... rest of the email sending code ...</code>

This approach correctly initializes the To and From properties during object instantiation, avoiding the read-only property assignment error. The complete corrected code would look like this:

<code class="language-csharp">using System.Net.Mail;

// ... other code ...

MailMessage mail = new MailMessage("[email protected]", "[email protected]");
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);</code>

By using the constructor to set these properties, the code will execute without errors. Remember to replace the placeholder email addresses with your actual sender and recipient addresses.

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