Can set relay name

src/main.rs

@@ -2,6 +2,7 @@ use clap::Parser;
 use lettre::message::header::ContentType;
 use lettre::message::Mailbox;
 use lettre::{Message, SmtpTransport, Transport};
+use lettre::transport::smtp::extension::ClientId;
 
 /// Simple mail sender
 #[derive(Parser, Debug)]
@@ -50,6 +51,10 @@ struct Args {
     /// Disable TLS
     #[arg(long)]
     disable_tls: bool,
+
+    /// Relay name
+    #[arg(long, default_value = "mail-out.mail.internal")]
+    smtp_relay_name: String,
 }
 
 fn main() {
@@ -81,6 +86,7 @@ fn main() {
         true => SmtpTransport::builder_dangerous(&args.smtp_domain),
         false => SmtpTransport::relay(&args.smtp_domain).unwrap(),
     };
+    mailer = mailer.hello_name(ClientId::Domain(args.smtp_relay_name));
     if let Some(port) = args.smtp_port {
         mailer = mailer.port(port);
     }