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# SMTP transport

This transport uses the SMTP protocol to send emails over the network (locally or remotely).

It is desinged to be:

- Secured: email are encrypted by default
- Modern: Unicode support for email content and sender/recipient adresses when compatible
- Fast: supports tcp connection reuse

This client is designed to send emails to a relay server, and should not be used to send emails directly to the destination.

The relay server can be the local email server, a specific host or a third-party service.

#### Simple example

This is the most basic example of usage:

use lettre::{SimpleSendableEmail, EmailTransport, EmailAddress, SmtpTransport}; let email = SimpleSendableEmail::new( EmailAddress::new("user@localhost".to_string()), vec![EmailAddress::new("root@localhost".to_string())], "message_id".to_string(), "Hello world".to_string(), ); // Open a local connection on port 25 let mut mailer = SmtpTransport::builder_unencrypted_localhost().unwrap().build(); // Send the email let result = mailer.send(&email); assert!(result.is_ok());

#### Complete example

use lettre::smtp::authentication::{Credentials, Mechanism}; use lettre::smtp::SUBMISSION_PORT; use lettre::{SimpleSendableEmail, EmailTransport, EmailAddress, SmtpTransport}; use lettre::smtp::extension::ClientId; use lettre::smtp::ConnectionReuseParameters; let email = SimpleSendableEmail::new( EmailAddress::new("user@localhost".to_string()), vec![EmailAddress::new("root@localhost".to_string())], "message_id".to_string(), "Hello world".to_string(), ); // Connect to a remote server on a custom port let mut mailer = SmtpTransport::simple_builder("server.tld".to_string()).unwrap() // Set the name sent during EHLO/HELO, default is `localhost` .hello_name(ClientId::Domain("my.hostname.tld".to_string())) // Add credentials for authentication .credentials(Credentials::new("username".to_string(), "password".to_string())) // Enable SMTPUTF8 if the server supports it .smtp_utf8(true) // Configure expected authentication mechanism .authentication_mechanism(Mechanism::Plain) // Enable connection reuse .connection_reuse(ConnectionReuseParameters::ReuseUnlimited).build(); let result_1 = mailer.send(&email); assert!(result_1.is_ok()); // The second email will use the same connection let result_2 = mailer.send(&email); assert!(result_2.is_ok()); // Explicitly close the SMTP transaction as we enabled connection reuse mailer.close();

#### Lower level

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

use lettre::EmailAddress; use lettre::smtp::SMTP_PORT; use lettre::smtp::client::Client; use lettre::smtp::client::net::NetworkStream; use lettre::smtp::extension::ClientId; use lettre::smtp::commands::*; let mut email_client: Client<NetworkStream> = Client::new(); let _ = email_client.connect(&("localhost", SMTP_PORT), None); let _ = email_client.smtp_command(EhloCommand::new(ClientId::new("my_hostname".to_string()))); let _ = email_client.smtp_command( MailCommand::new(Some(EmailAddress::new("user@example.com".to_string())), vec![]) ); let _ = email_client.smtp_command( RcptCommand::new(EmailAddress::new("user@example.org".to_string()), vec![]) ); let _ = email_client.smtp_command(DataCommand); let _ = email_client.message(Box::new("Test email".as_bytes())); let _ = email_client.smtp_command(QuitCommand);