Problem with Mailbox

Many thanks. Is it to ensure 587 port is open there?



Yes, I am putting the administrator password below

                    ...
                    SmtpClient client = new SmtpClient("my-friend.co", 587);
                    client.DeliveryMethod = SmtpDeliveryMethod.Network;
                    client.UseDefaultCredentials = true;
                    client.Credentials = new System.Net.NetworkCredential("Administrator@my-friend.co", "????");
                    ...

right now, I still get this exception and stacktrace.

Mailbox unavailable. The server response was: 5.7.1 Unable to relay

at System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressCollection recipients, String deliveryNotify, Boolean allowUnicode, SmtpFailedRecipientException& exception)

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Many Thanks & Best Regards, Hua Min