Rust

Before you start

• Rust 1.70 or later
• lettre 0.11

1Add lettre

[dependencies]
lettre = "0.11"

2Send a test message

use lettre::transport::smtp::authentication::Credentials;
use lettre::{Message, SmtpTransport, Transport};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let email = Message::builder()
        .from("staging@example.com".parse()?)
        .to("anyone@example.com".parse()?)
        .subject("Sandbox check")
        .body(String::from("Hello from Rust."))?;

    let credentials = Credentials::new(
        "mc_0000000000000000".to_owned(),
        "pw_0000000000000000".to_owned(),
    );

    let mailer = SmtpTransport::starttls_relay("smtp.mailclutch.com")?
        .port(587)
        .credentials(credentials)
        .build();

    mailer.send(&email)?;
    Ok(())
}

Watch it land

Open the sandbox and the message is there — rendered HTML, plain text, raw source, attachments, and the SPF, DKIM and DMARC verdicts. It updates live, so you can leave it open next to your terminal.

Nothing is ever delivered onward, whatever address you send to; claim the inbox with an account and it stays.

What usually goes wrong

• starttls_relay or relay

  starttls_relay connects in the clear and upgrades — that is port 587. relay is implicit TLS on 465. Pick one; mixing them is the usual cause of a handshake error.

• Async

  AsyncSmtpTransport with the tokio1-native-tls feature takes the same builder, and send becomes .await.

Other stacks

The same four values in another dialect. Every guide below is filled in with the sandbox pair at the top of this page.