C# Failed to send emails using Smtpclient

Question

I am getting the following error while running the system on the server with port 587: Mailbox not available

Error stack:

When I change the door to 465 and Smtpserver.Enablessl = true; timeout occurs;

I run the same system on my local machine and it works normally with port 587.

Source code used:

MailMessage mail = new MailMessage();
SmtpClient SmtpServer = new SmtpClient("host");
mail.From = new MailAddress("email");
mail.To.Add("to");
mail.Subject = "teste"
mail.Body = "teste";

SmtpServer.Port = 587;
SmtpServer.Credentials = new 
System.Net.NetworkCredential("login", "senha");
SmtpServer.EnableSsl = false;
SmtpServer.Send(mail);