[][src]Crate lettre

Lettre is a mailer written in Rust. It provides a simple email builder and several transports.


This mailer is divided into:

  • An email part: builds the email message
  • A transport part: contains the available transports for your emails. To be sendable, the emails have to implement SendableEmail.

Creating messages

The email part builds email messages. For now, it does not support attachments. An email is built using an EmailBuilder. The simplest email could be:

use lettre::email::EmailBuilder;

// Create an email
let email = EmailBuilder::new()
    // Addresses can be specified by the tuple (email, alias)
    .to(("user@example.org", "Firstname Lastname"))
    // ... or by an address only
    .subject("Hi, Hello world")
    .text("Hello world.")


When the build method is called, the EmailBuilder will add the missing headers (like Message-ID or Date) and check for missing necessary ones (like From or To). It will then generate an Email that can be sent.

The text() method will create a plain text email, while the html() method will create an HTML email. You can use the alternative() method to provide both versions, using plain text as fallback for the HTML version.

Below is a more complete example, not using method chaining:

use lettre::email::EmailBuilder;

let mut builder = EmailBuilder::new();
builder.add_to(("user@example.org", "Alias name"));
builder.add_cc(("user@example.net", "Alias name"));
builder.set_subject("Hello world");
builder.set_alternative("<h2>Hi, Hello world.</h2>", "Hi, Hello world.");
builder.add_header(("X-Custom-Header", "my header"));

let email = builder.build();

See the EmailBuilder documentation for a complete list of methods.

Sending messages

The following sections describe the available transport methods to handle emails.

  • The SmtpTransport uses the SMTP protocol to send the message over the network. It is the prefered way of sending emails.
  • The FileTransport creates a file containing the email content to be sent. It can be used for debugging or if you want to keep all sent emails.
  • The StubTransport is useful for debugging, and only prints the content of the email in the logs.

SMTP transport

This SMTP follows RFC 5321, but is still a work in progress. It is designed to efficiently send emails from an application to a relay email server, as it relies as much as possible on the relay server for sanity and RFC compliance checks.

It implements the following extensions:

Simple example

This is the most basic example of usage:

use lettre::transport::smtp::{SmtpTransport, SmtpTransportBuilder};
use lettre::email::EmailBuilder;
use lettre::transport::EmailTransport;

let email = EmailBuilder::new()
                    .body("Hello World!")

// Open a local connection on port 25
let mut mailer =
// Send the email
let result = mailer.send(email);


Complete example

use lettre::email::EmailBuilder;
use lettre::transport::smtp::{SecurityLevel, SmtpTransport,
use lettre::transport::smtp::authentication::Mechanism;
use lettre::transport::smtp::SUBMISSION_PORT;
use lettre::transport::EmailTransport;

let email = EmailBuilder::new()
                    .body("Hello World!")

// Connect to a remote server on a custom port
let mut mailer = SmtpTransportBuilder::new(("server.tld",
    // Set the name sent during EHLO/HELO, default is `localhost`
    // Add credentials for authentication
    .credentials("username", "password")
    // Specify a TLS security level. You can also specify an SslContext with
    // .ssl_context(SslContext::Ssl23)
    // Enable SMTPUTF8 if the server supports it
    // Configure expected authentication mechanism
    // Enable connection reuse

let result_1 = mailer.send(email.clone());

// The second email will use the same connection
let result_2 = mailer.send(email);

// Explicitly close the SMTP transaction as we enabled connection reuse

Lower level

You can also send commands, here is a simple email transaction without error handling:

use lettre::transport::smtp::SMTP_PORT;
use lettre::transport::smtp::client::Client;
use lettre::transport::smtp::client::net::NetworkStream;

let mut email_client: Client<NetworkStream> = Client::new();
let _ = email_client.connect(&("localhost", SMTP_PORT), None);
let _ = email_client.ehlo("my_hostname");
let _ = email_client.mail("user@example.com", None);
let _ = email_client.rcpt("user@example.org");
let _ = email_client.data();
let _ = email_client.message("Test email");
let _ = email_client.quit();

Stub transport

The stub transport only logs message envelope and drops the content. It can be useful for testing purposes.

use lettre::transport::stub::StubEmailTransport;
use lettre::transport::EmailTransport;
use lettre::email::EmailBuilder;

let email = EmailBuilder::new()
                    .body("Hello World!")

let mut sender = StubEmailTransport;
let result = sender.send(email);

Will log the line:

b7c211bc-9811-45ce-8cd9-68eab575d695: from=<user@localhost> to=<root@localhost>

File transport

The file transport writes the emails to the given directory. The name of the file will be message_id.txt. It can be useful for testing purposes, or if you want to keep track of sent messages.

use std::env::temp_dir;

use lettre::transport::file::FileEmailTransport;
use lettre::transport::EmailTransport;
use lettre::email::{EmailBuilder, SendableEmail};

// Write to the local temp directory
let mut sender = FileEmailTransport::new(temp_dir());
let email = EmailBuilder::new()
                .body("Hello World!")

let result = sender.send(email);

Example result in /tmp/b7c211bc-9811-45ce-8cd9-68eab575d695.txt:

b7c211bc-9811-45ce-8cd9-68eab575d695: from=<user@localhost> to=<root@localhost>
To: <root@localhost>
From: <user@localhost>
Subject: Hello
Date: Sat, 31 Oct 2015 13:42:19 +0100
Message-ID: <b7c211bc-9811-45ce-8cd9-68eab575d695.lettre@localhost>

Hello World!



Simple email representation


Represents an Email transport