Why do I get 5.5.4 Invalid Address error?

Question

I tried to send an email using the following code:

MailMessage message = new MailMessage();

        message.From = new MailAddress(fromMailAddress.Trim());
        message.To.Add(new MailAddress(toMailAddress.Trim()));

        message.Subject = subject;
        message.Body = body;
        message.SubjectEncoding = System.Text.Encoding.UTF8;
        message.BodyEncoding = System.Text.Encoding.UTF8;
        SmtpClient client = new SmtpClient();
        try
        {
            client.Send(message);
        }
        catch(Exception e)
        {
            throw e;
        }

However, I got the exception:

The server response was: 5.5.4 Invalid Address

The from email, to email, server host name and port are all correct. The exact same code, with exact same input values works on another machine in our office

Answer 1

Found out the answer after some thorough debugging.

Turns out my machine name has an 'å'-character (invalid Swedish character) in it. After changing that, it worked.

Answer 2

There was a KB released for System.Net.Mail that affected address parsing and Unicode so the reason it worked on one machine and not the other was likely the presence of this KB. .NET 4.0 also has some significant improvements in parsing email addresses.