You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: autoconfigure.rs
    path of file: ./repos/lettre/examples
    
    the code of the file until where you have to start completion: use std::{env, process, time::Duration};

use lettre::SmtpTransport;

fn main() {
    tracing_subscriber::fmt::init();

    let smtp_host = match env::args().nth(1) {
        Some(smtp_host) => smtp_host,
        None => {
            println!("Please provide the SMTP host as the firs
    
fn main() {
    tracing_subscriber::fmt::init();

    let smtp_host = match env::args().nth(1) {
        Some(smtp_host) => smtp_host,
        None => {
            println!("Please provide the SMTP host as the first argument to this command");
            process::exit(1);
        }
    };

    // TLS wrapped connection
    {
        tracing::info!(
            "Trying to establish a TLS wrapped connection to {}",
            smtp_host
        );

        let transport = SmtpTransport::relay(&smtp_host)
            .expect("build SmtpTransport::relay")
            .timeout(Some(Duration::from_secs(10)))
            .build();
        match transport.test_connection() {
            Ok(true) => {
                tracing::info!("Successfully connected to {} via a TLS wrapped connection (SmtpTransport::relay). This is the fastest option available for connecting to an SMTP server", smtp_host);
            }
            Ok(false) => {
                tracing::error!("Couldn't connect to {} via a TLS wrapped connection. No more information is available", smtp_host);
            }
            Err(err) => {
                tracing::error!(err = %err, "Couldn't connect to {} via a TLS wrapped connection", smtp_host);
            }
        }
    }

    println!();

    // Plaintext connection which MUST then successfully upgrade to TLS via STARTTLS
    {
        tracing::info!("Trying to establish a plaintext connection to {} and then updating it via the SMTP STARTTLS extension", smtp_host);

        let transport = SmtpTransport::starttls_relay(&smtp_host)
            .expect("build SmtpTransport::starttls_relay")
            .timeout(Some(Duration::from_secs(10)))
            .build();
        match transport.test_connection() {
            Ok(true) => {
                tracing::info!("Successfully connected to {} via a plaintext connection which then got upgraded to TLS via the SMTP STARTTLS extension (SmtpTransport::starttls_relay). This is the second best option after the previous TLS wrapped option", smtp_host);
            }
            Ok(false) => {
                tracing::error!(
                    "Couldn't connect to {} via STARTTLS. No more information is available",
                    smtp_host
                );
            }
            Err(err) => {
                tracing::error!(err = %err, "Couldn't connect to {} via STARTTLS", smtp_host);
            }
        }
    }

    println!();

    // Plaintext connection (very insecure)
    {
        tracing::info!(
            "Trying to establish a plaintext connection to {}",
            smtp_host
        );

        let transport = SmtpTransport::builder_dangerous(&smtp_host)
            .timeout(Some(Duration::from_secs(10)))
            .build();
        match transport.test_connection() {
            Ok(true) => {
                tracing::info!("Successfully connected to {} via a plaintext connection. This option is very insecure and shouldn't be used on the public internet (SmtpTransport::builder_dangerous)", smtp_host);
            }
            Ok(false) => {
                tracing::error!(
                    "Couldn't connect to {} via a plaintext connection. No more information is available",
                    smtp_host
                );
            }
            Err(err) => {
                tracing::error!(err = %err, "Couldn't connect to {} via a plaintext connection", smtp_host);
            }
        }
    }
}