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: mod.rs
    path of file: ./repos/lettre/src/transport/file
    
    the code of the file until where you have to start completion: //! The file transport writes the emails to the given directory. The name of the file will be
//! `message_id.eml`.
//! It can be use
    
//! # fn main() -> Result<(), Box<dyn Error>> {
//! use std::env::temp_dir;
//!
//! use lettre::{FileTransport, Message, Transport};
//!
//! // Write to the local temp directory
//! let sender = FileTransport::new(temp_dir());
//! let email = Message::builder()
//!     .from("NoBody <nobody@domain.tld>".parse()?)
//!     .reply_to("Yuin <yuin@domain.tld>".parse()?)
//!     .to("Hei <hei@domain.tld>".parse()?)
//!     .subject("Happy new year")
//!     .body(String::from("Be happy!"))?;
//!
//! let result = sender.send(&email);
//! assert!(result.is_ok());
//! # Ok(())
//! # }