C#

public delegate void UpdateSelectionDelegate(int start, int length);
private TextBox textBox;
private MenuItem menuCopy;
private MenuItem menuCut;
 
public void UpdateSelection(int start, int length) {
	if (InvokeRequired) {
		// this method calls itself, in order for it run on UI thread
		Invoke(new UpdateSelectionDelegate(UpdateSelection),
			new object[]{start, length});
	} else {
		// adjust here whatever control needs updated on the user interface
		textBox.Select(start, length);
		menuCopy.Enabled=length!=0;
		menuCut.Enabled=length!=0;
	}
}

using System.Net.Mail;
...

SmtpClient smtpClient = new SmtpClient("smtp.myisp.com");
smtpClient.Send("tome@me.com", 
    "fromyou@you.com", 
    "Hello Word", 
    "This is the message");