Crate mailstrom [] [src]

Mailstrom handles email delivery in a background worker thread, with the following features:

  • Accepts an email from the caller and then does everything necessary to get it delivered to all recipients without blocking the caller.
  • Allows the caller to query the status of an earlier submitted email at any time, to determine if it is Queued, Delivered, Deferred, or has Failed, with details as to why, on a per-recipient basis.
  • Handles all parsing, validation, and encoding of email content and headers, in compliance with RFC 5322 (and other RFCs). Uses the email-format library for this.
  • Looks up the DNS MX records of the recipients, and delivers directly to those Internet mail servers over SMTP, thus not requiring any local SMTP relay. Uses the resolv library for DNS lookups (via your operating system)
  • SMTP transport "heavy lifting" is performed via the lettre library. Uses STARTTLS where available.
  • Retries with exponential backoff for a fixed number of retries (currently fixed at 3), when the send result is Deferred
  • Uses a pluggable user-defined state management (persistence) layer.


  • Only works on glibc based operating systems, due to usage of the resolv library.
  • The email-format crate is somewhat incomplete and clunky still. It doesn't incorporate RFC 6854 (updated From and Sender syntax) yet. It defines types one-to-one with ABNF parsing units, rather than as semantic units of meaning. And it doesn't let you use obvious types yet like setting the date from a DateTime type. However, these issues will be worked out in the near future.

You can use it as follows:

extern crate email_format;
extern crate mailstrom;

use email_format::Email;
use mailstrom::{Mailstrom, Config, MemoryStorage};

fn main() {
    let mut email = Email::new(
        "",  // "From:"
        "Wed, 05 Jan 2015 15:13:05 +1300" // "Date:"

    email.set_reply_to("My Mailer <>").unwrap();
    email.set_to("You <>, AndYou <>").unwrap();
    email.set_cc("Our Friend <>").unwrap();
    email.set_subject("Hello Friend").unwrap();
    email.set_body("Good to hear from you.\r\n\
                    I wish you the best.\r\n\
                    Your Friend").unwrap();

    let mut mailstrom = Mailstrom::new(
        Config {
            helo_name: "".to_owned(),

    let message_id = mailstrom.send_email(email).unwrap();

    // Later on, after the worker thread has had time to process the request,
    // you can check the status:

    let status = mailstrom.query_status(&*message_id).unwrap();
    println!("{:?}", status);


pub use status::Status;
pub use status::DeliveryResult;



This is exposed for implementers of MailstromStorage but otherwise should not be needed by users of this library.








A trait for implementing Mailstrom storage