Programming language: Rust
License: MIT License
Tags: Smtp     Mailer     Email    
Latest version: v0.10.1

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lettre A mailer library for Rust


Lettre provides the following features:

  • Multiple transport methods
  • Unicode support (for email content and addresses)
  • Secure delivery with SMTP using encryption and authentication
  • Easy email builders
  • Async support

Lettre does not provide (for now):

  • Email parsing

Supported Rust Versions

Lettre supports all Rust versions released in the last 6 months. At the time of writing the minimum supported Rust version is 1.56, but this could change at any time either from one of our dependencies bumping their MSRV or by a new patch release of lettre.


This library requires Rust 1.56.0 or newer. To use this library, add the following to your Cargo.toml:

lettre = "0.10"
use lettre::transport::smtp::authentication::Credentials;
use lettre::{Message, SmtpTransport, Transport};

let email = Message::builder()
    .from("NoBody <[email protected]>".parse().unwrap())
    .reply_to("Yuin <[email protected]>".parse().unwrap())
    .to("Hei <[email protected]>".parse().unwrap())
    .subject("Happy new year")
    .body(String::from("Be happy!"))

let creds = Credentials::new("smtp_username".to_string(), "smtp_password".to_string());

// Open a remote connection to gmail
let mailer = SmtpTransport::relay("smtp.gmail.com")

// Send the email
match mailer.send(&email) {
    Ok(_) => println!("Email sent successfully!"),
    Err(e) => panic!("Could not send email: {:?}", e),

Not sure of which connect options to use?

Clone the lettre git repository and run the following command (replacing SMTP_HOST with your SMTP server's hostname)

cargo run --example autoconfigure SMTP_HOST


The lettre tests require an open mail server listening locally on port 2525 and the sendmail command. If you have python installed such a server can be launched with python -m smtpd -n -c DebuggingServer

Alternatively only unit tests can be run by doing cargo test --lib.


These are general steps to be followed when troubleshooting SMTP related issues.

  • Ensure basic connectivity, ensure requisite ports are open and daemons are listening.
  • Confirm that your service provider allows traffic on the ports being used for mail transfer.
  • Check SMTP relay authentication and configuration.
  • Validate your DNS records. (DMARC, SPF, DKIM, MX)
  • Verify your SSL/TLS certificates are setup properly.
  • Investigate if filtering, formatting, or filesize limits are causing messages to be lost, delayed, or blocked by relays or remote hosts.

Code of conduct

Anyone who interacts with Lettre in any space, including but not limited to this GitHub repository, must follow our code of conduct.


This program is distributed under the terms of the MIT license.

The builder comes from emailmessage-rs by Kayo, under MIT license.

See [LICENSE](./LICENSE) for details.

*Note that all licence references and agreements mentioned in the lettre README section above are relevant to that project's source code only.