C# String.Trim() not removing characters from MailMessage.Subject

I'm trying to eliminate certain symbols from the Subject property of a MailMessage object. What I'm experiencing is that it does nothing. Even after assigning Subject to a string, and trimming that, the final Subject still has the symbols in it. (not showed in example)

MailMessage mailMessage = new MailMessage
{
    From = new MailAddress(mail.SenderEmailAddress),
    SubjectEncoding = System.Text.Encoding.UTF8,
    Subject = mail.Subject.Trim(new char[] {}), //symbol list, like ":", "~", ">"
    Body = mail.Body
};

String path = @"C:\Users\" + Environment.UserName + @"\Documents\EML\";

if (!Directory.Exists(path))
{
    Directory.CreateDirectory(path);
}

path = @"C:\Users\" + Environment.UserName + @"\Documents\EML\"
    + mailMessage.Subject + ".eml";

MessageBox.Show(path);

The message box is just to see whether the symbol gets removed or not at the moment, path will be put into a method later.

mail has subject RE: dog, .Trim tries to remove :,

MessageBox shows C:\Users\user\Documents\EML\RE: dog.eml.

Solution

From MSDN:

String.Trim Method () - Removes all leading and trailing white-space characters from the current String object.

So, Trim isn't going to remove characters from the middle of a String. Commenters suggested using Replace instead, but there isn't a signature that takes an array of characters like you are using. An easy way around that is Extension methods.

    class Program
    {

        static void Main(string[] args)
        {
            string text = "This:is~a>test";
            string subject = text.ReplaceFromCollection(new char[] { ':', '~', '>'}); //symbol list, like ":", "~", ">"

            Console.WriteLine($"{text}\n{subject}");
            Console.ReadLine();
        }

    }

    static class Extensions
    {
        public static String ReplaceFromCollection(this string text, IEnumerable<char> characters)
        {
            foreach (var chr in characters)
            {
                text = text.Replace(chr.ToString(), String.Empty);
            }
            return text;
        }
    }

Using this, each character in your string that matches a character in the array is replaced with the empty String one by one. The result is then passed back.