unable to send emails using port 25 in ssl mode?

Question

Hi I am developing web application in mvc5 c#. I have hosted my website in ssl mode. I am using below code to send emails in production server.

                string AdminEmail = ConfigurationManager.AppSettings["AdminEmail"].ToString();
                MailMessage mail = new MailMessage();
                mail.To.Add(emailid);
                mail.Bcc.Add(AdminEmail);
                mail.From = new MailAddress(MailID);
                mail.Subject = Subject;
                mail.Body = Body;
                mail.IsBodyHtml = true;
                SmtpClient smtp = new SmtpClient(hostserver);
                smtp.Credentials = new System.Net.NetworkCredential
                 (MailID, Password);
                smtp.Send(mail);
                return 1;

i added

   if (IsInternalBuild)
                {
                    smtp.Host = hostserver;    mail.c3payroll.com
                    smtp.Port = Convert.ToInt32(portno);  465
                    smtp.UseDefaultCredentials = true;
                    smtp.EnableSsl = true;
                }

IsInternalBuild is true in production environment.

When sending in ssl mode, do i need to change anything in above code? Can someone help me to implement this? Any help would be appreciated. Thank you.

Answer 1

Depending on your email host provider settings, it's easy to set host name, port number and SSL feature to sending mail by using corresponding properties in SmtpClient:

SmtpClient smtp = new SmtpClient(hostserver);
smtp.DeliveryMethod = SmtpDeliveryMethod.Network;
smtp.Credentials = new System.Net.NetworkCredential(MailID, Password);
smtp.Host = hostserver; // host name as mail server
smtp.Port = Convert.ToInt32(portno); // some hosts doesn't support port 25 for SMTPS, try this port instead or use 587
smtp.EnableSsl = true; // use SSL configuration

smtp.Send(mail);

Update (Explicit & Implicit SSL)

Keep in mind that System.Net.Mail.SmtpClient only supports explicit SSL, which requires insecure connection to SMTP server over port 25 to negotiate with TLS. There is SMTP over SSL for port 465 which requires TLS negotiation before connection to SMTP server established, but still doesn't support implicit SSL with standard System.Net.Mail library. The reason is explained at this reference.

There is no way to use Implicit SSL (SMTPS) with System.Net.Mail. Implicit SSL would have the entire connection is wrapped in an SSL layer. A specific port would be used (port 465 is common). There is no formal RFC covering Implicit SSL.

Implicit SSL would go something like: Start SSL (start encryption) -> Connect -> Authenticate -> send data

This is not considered a bug, it’s by design. There are two types of SSL authentication for SMTP, and we only support one with System.Net.Mail (by design) – Explicit SSL.

To use implicit SSL, you need to utilize libraries which enables CDOSYS, such like System.Web.Mail.MailMessage and System.Web.Mail.SmtpMail (which seems to be obsolete but works with both explicit and implicit SSL, require CDO configuration schemas to work):

System.Web.Mail.MailMessage mail = new System.Web.Mail.MailMessage();
mail.To = emailid;
mail.Bcc = AdminEmail;
mail.From = new MailAddress(MailID);
mail.Subject = Subject;
mail.Body = Body;
mail.BodyEncoding = System.Text.Encoding.UTF8;
mail.BodyFormat = System.Web.Mail.MailFormat.Html;
mail.Fields.Add("http://schemas.microsoft.com/cdo/configuration/smtpserver", hostServer);
mail.Fields.Add("http://schemas.microsoft.com/cdo/configuration/smtpserverport", 25);
mail.Fields.Add("http://schemas.microsoft.com/cdo/configuration/sendusing", 2);
mail.Fields.Add("http://schemas.microsoft.com/cdo/configuration/smtpusessl", true);
mail.Fields.Add("http://schemas.microsoft.com/cdo/configuration/smtpauthenticate", 1);
mail.Fields.Add("http://schemas.microsoft.com/cdo/configuration/sendusername", MailID);
mail.Fields.Add("http://schemas.microsoft.com/cdo/configuration/sendpassword", Password);

System.Web.Mail.SmtpMail.SmtpServer = hostServer;
System.Web.Mail.SmtpMail.Send(mail);

Related issue:

How can I send emails through SSL SMTP with the .NET Framework?

Answer 2

You cant send SSL emails on port 25, you need to use port 465 instead

You also need to set smtp.EnableSsl = true