Sending email leads to an os error (invalid token) about lettre HOT 6 OPEN

    // Build the message
    let email = Message::builder()
        .from(from_mailbox)
        .to(to_mailbox)
        .subject(subject)
        .multipart(
            MultiPart::alternative() // This is composed of two parts.
                .singlepart(
                    SinglePart::builder()
                        .header(header::ContentType::TEXT_PLAIN)
                        .body(String::from(body_txt)), // Every message should have a plain text fallback.
                )
                .singlepart(
                    SinglePart::builder()
                        .header(header::ContentType::TEXT_HTML)
                        .body(String::from(body_html)),
                ),
        )
        .unwrap();

    // Setup credentials
    let creds = Credentials::new(SETTINGS.smtp_user.clone(), SETTINGS.smtp_password.clone());

    // Open SMTP connection
    let mailer = AsyncSmtpTransport::<Tokio1Executor>::relay(&SETTINGS.smtp_host)
        .unwrap()
        .credentials(creds)
        .port(SETTINGS.smtp_port)
        .build();

    // Send the email
    let send_result = mailer.send(email).await;