How to use a proxy?

[diudiu1]

https://stackoverflow.com/questions/844835/sending-mail-through-http-proxy

I found a way to use a proxy from this answer, but the email was not sent successfully after I used it. I'm sure my proxy address is correct because my http proxy for another service also uses this address;

            using (var client = new SmtpClient())
            {
                if (!string.IsNullOrWhiteSpace(proxyUrl))
                {
                    if (proxyUrl.IndexOf("://") == -1)
                    {
                        proxyUrl = "http://" + proxyUrl;
                    }
                    var uri= new Uri(proxyUrl);
                    client.ProxyClient = new HttpProxyClient(uri.Host, uri.Port);
                }
               
                await client.ConnectAsync(mailServer, mailServerPort, SecureSocketOptions.None);
                await client.AuthenticateAsync(sendAccount, sendPassword);

                await client.SendAsync(message);
                await client.DisconnectAsync(true);
            }