Mailkit SMTP - StartTLS & TLS flags

Question

I am trying to connect to iCloud via SmtpClient

The settings I am using are as follows:

Server name: smtp.mail.me.com
SSL Required: Yes
If you see an error message when using SSL, try using TLS or STARTTLS instead.
Port: 587
SMTP Authentication Required: Yes - with relevant username and password

If I use SSL I get "Handshake failed due to unexpected packet format"

If I don't use SSL visual studio debugger hangs on connect.

I think the problem is I am not telling the SmtpClient to use tls but I cant find documentation on how to do this.

The code is as follows:

using (var client = new SmtpClient()) {
    client.Timeout = 1000 * 20;
    //client.Capabilities.
    client.AuthenticationMechanisms.Remove ("XOAUTH2");

    client.Connect("SMTP.mail.me.com", 587, false); //dies here
    //client.Connect(servername, port, useSsl);
    //can I set tls or starttls here??
    client.Authenticate(username, password);
    client.Send(FormatOptions.Default, message);
}

Am I able to set TLS or StartTLS manually. One thing I did try is the following but it did not seem to work

client.Connect(new Uri("smtp://" + servername + ":" + port + "/?starttls=true"));

Thanks for any help with this.

Answer 1

The Connect() method that you are using only allows enabling/disabling SSL-wrapped connections which is not the same thing as StartTLS.

Due to the confusion, I've implemented a separate Connect() method that makes this more obvious what is going on:

using (var client = new SmtpClient()) {
    // Note: don't set a timeout unless you REALLY know what you are doing.
    //client.Timeout = 1000 * 20;

    client.Connect ("smtp.mail.me.com", 587, SecureSocketOptions.StartTls);
    client.Authenticate (username, password);
    client.Send (message);
}

Try that.

Answer 2

You can set your options to "SecureSocketOptions.Auto" something like this

await client.ConnectAsync(mailService.Host, mailService.Port,   SecureSocketOptions.Auto);

MailKit will automatically decide to use SSL or TLS.