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: config.rs
    path of file: ./repos/bionic-gpt/crates/axum-server/src
    
    the code of the file until where you have to start completion: use lettre::message;
use std::env;

#[derive(Clone, Debug)]
pub struct SmtpConfig {
    // Configure SMTP for email.
    pub host: St
    
    pub fn new() -> Option<SmtpConfig> {
        let host = env::var("SMTP_HOST");
        let username = env::var("SMTP_USERNAME");
        let password = env::var("SMTP_PASSWORD");
        let smtp_port = env::var("SMTP_PORT");
        let domain = env::var("INVITE_DOMAIN");
        let from_email = env::var("INVITE_FROM_EMAIL_ADDRESS");
        let unstructured_endpoint = if let Ok(domain) = env::var("UNSTRUCTURED_ENDPOINT") {
            domain
        } else {
            "http://unstructured:8000".to_string()
        };

        if let (Ok(host), Ok(username), Ok(password), Ok(smtp_port), Ok(domain), Ok(from_email)) =
            (host, username, password, smtp_port, domain, from_email)
        {
            Some(SmtpConfig {
                host,
                port: smtp_port.parse::<u16>().unwrap(),
                tls_off: env::var("SMTP_TLS_OFF").is_ok(),
                username,
                password,
                domain,
                unstructured_endpoint,
                from_email: from_email.parse().unwrap(),
            })
        } else {
            None
        }
    }