Pfthb

When I run the following command in the terminal

openssl s_client -connect gmail-smtp-in.l.google.com:25 -starttls smtp

I get a CONNECTED(00000005) response.

I am trying to achieve the same connection with Rust using rust-openssl (I am open to other libraries though), and here's what I have:

extern crate openssl;

use openssl::ssl::SslConnector, SslMethod;

use std::net::TcpStream;

fn main() 
 let connector = SslConnector::builder(SslMethod::tls()).unwrap().build();
 let stream = TcpStream::connect("gmail-smtp-in.l.google.com:25").unwrap();
 let e = connector
 .connect("gmail-smtp-in.l.google.com", stream)
 .unwrap_err();
 eprintln!(":#?", e);

However, the response I get is:

Failure(
 MidHandshakeSslStream 
 stream: SslStream 
 stream: TcpStream 
 addr: V6(
 [2001:41d0:a:2346::1]:57190
 ),
 peer: V6(
 [2a00:1450:400c:c0c::1b]:25
 ),
 fd: 3
 ,
 ssl: Ssl 
 state: "SSLv3/TLS write client hello",
 verify_result: X509VerifyResult 
 code: 0,
 error: "ok"
 
 
 ,
 error: Error 
 code: ErrorCode(
 1
 ),
 cause: Some(
 Ssl(
 ErrorStack(
 [
 Error 
 code: 336130315,
 library: "SSL routines",
 function: "ssl3_get_record",
 reason: "wrong version number",
 file: "ssl/record/ssl3_record.c",
 line: 252
 
 ]
 )
 )
 )
 
 
)

I'm guessing I'm missing the -starttls smtp part in the Rust code, but can't figure out how to add it.

Take a more detailed look in the openssl-sources on what -starttls smtp actually does, and replay that in Rust? It will just be a few library calls, but first you need to speak STMP to your server, and then switch to TLS. (Maybe that's already bundled up in the openssl-library in a single call.)