dox_mailer 3.0.0-alpha.2

Send email from the Dox framework: SMTP, Amazon SES, Azure, Resend, Mailgun, Postmark and sendmail.

dox_mailer

Send email from the Dox framework: SMTP, Amazon SES, Azure, Resend, Mailgun, Postmark and sendmail.

You write a Message and call Mail.send(). A transport sends it. You pick the transport in a config file, so you can change providers with no code change.

The package has its own SMTP client, AWS signer and MIME builder. Next to dox_core, it only needs http and crypto.

Install

dart pub add dox_mailer

Set up

1. Config

A mailer is a name and a transport. defaultMailer is the one that Mail.send() uses.

lib/config/mail.dart:

import 'package:dox_core/dox_core.dart';
import 'package:dox_mailer/dox_mailer.dart';

MailConfig mailConfig = MailConfig(
  /// the mailer of Mail.send()
  defaultMailer: Env.get('MAIL_MAILER', 'log'),

  /// for messages with no from address
  from: Address(Env.get('MAIL_FROM', '[e-mail]'), 'My app'),

  mailers: <String, Transport>{
    'smtp': SmtpTransport(
      host: Env.get('MAIL_HOST', 'localhost'),
      port: Env.get<int>('MAIL_PORT', 587),
      username: Env.get<String?>('MAIL_USERNAME'),
      password: Env.get<String?>('MAIL_PASSWORD'),
    ),

    /// prints emails, sends nothing
    'log': LogTransport(),
  },
);

Env.get() reads the .env file and the real environment. You can also add the keys to the AppEnv class of your app and use env.mailHost.

.env:

MAIL_MAILER=smtp
MAIL_FROM=[e-mail]
MAIL_HOST=smtp.example.com
MAIL_PORT=587
MAIL_USERNAME=me
MAIL_PASSWORD=secret

Option	Default	What it does
defaultMailer	log	the mailer of Mail.send()
mailers	a log mailer	each mailer name and its transport
from	none	the from address of a message that has none
replyTo	none	the reply-to addresses of a message that has none

2. Provider

The service sets up the mailers in every isolate. Put it in lib/ so the generated container finds it.

lib/providers/mail_provider.dart:

import 'package:dox_mailer/dox_mailer.dart';

import '../config/mail.dart';

/// Sets up the mailers. Dox finds every DoxProvider class,
/// see lib/generated/container.g.dart.
class AppMailProvider extends MailProvider {
  AppMailProvider() : super(mailConfig);
}

When the server stops, the service closes open SMTP connections and HTTP clients.

Send an email

import 'package:dox_mailer/dox_mailer.dart';

await Mail.send(
  Message(
    to: <Address>[Address('[e-mail]', 'Ann Lee')],
    subject: 'Welcome',
    text: 'Hello Ann, welcome!',
    html: '<p>Hello Ann, <b>welcome</b>!</p>',
  ),
);

Send with another mailer:

await Mail.mailer('ses').send(message);

send() gives a SentMessage. Its messageId is the id of the provider (or the Message-ID header for SMTP and sendmail).

When the message can not be sent, send() throws a MailException. It has the statusCode and the body of the answer of the server.

The message

Field	What it is
from	an Address. Null: MailConfig.from
to, cc, bcc	lists of Address
replyTo	a list of Address
subject	text
text	the plain text body
html	the HTML body
attachments	a list of Attachment
headers	extra headers, like {'X-Campaign': 'fall'}
tags	tags for the reports of the provider
metadata	key and value data for the provider, like {'user_id': '42'}

An Address is an email and an optional name: Address('[e-mail]', 'Ann'). Address.parse('Ann <[e-mail]>') reads one from text.

A message needs a from address, at least one recipient, and a text or HTML body. A subject or header with a line break is an error, so user input can not add headers.

Attachments

Message(
  to: <Address>[Address('[e-mail]')],
  subject: 'Your invoice',
  text: 'The invoice is attached.',
  attachments: <Attachment>[
    Attachment(pdfBytes, 'invoice.pdf'),
    Attachment.fromFile('storage/terms.pdf'),
  ],
);

The content type comes from the file extension. Pass contentType to set it.

Inline images

Give the file a cid. Use it in the HTML with cid:.

Message(
  to: <Address>[Address('[e-mail]')],
  subject: 'Hello',
  html: '<img src="cid:logo.png"> Hello!',
  attachments: <Attachment>[
    Attachment.fromFile('assets/logo.png', cid: 'logo.png'),
  ],
);

Mailgun uses the file name as the cid. So for Mailgun, use a cid like logo.png, with the file extension.

HTML from a view

With dox_view, render a template to HTML:

String html = View.render('emails/welcome', <String, dynamic>{'name': 'Ann'});
await Mail.send(Message(to: to, subject: 'Welcome', html: html));

Transports

SMTP

'smtp': SmtpTransport(
  host: 'smtp.example.com',
  port: 587,
  username: Env.get('MAIL_USERNAME'),
  password: Env.get('MAIL_PASSWORD'),
  encryption: SmtpEncryption.starttls,
),

Option	Default	What it does
host	required	the server
port	465 for tls, 587 for starttls, 25 for none	the port
username, password	none	the login. No username: no login
encryption	starttls	none, starttls (switch to TLS after connect) or tls (TLS from the start)
allowInsecure	false	accept a self-signed TLS certificate. Only for test servers
auth	PLAIN, or LOGIN when the server has no PLAIN	SmtpAuth.plain, SmtpAuth.login or SmtpAuth.xoauth2
localDomain	localhost	the name of this machine, for EHLO
timeout	30 seconds	the time to connect, and to wait for each reply
keepAlive	false	keep the connection open for the next message

With starttls, the send fails when the server does not offer STARTTLS. Your password is never sent in plain text by mistake.

For Gmail or Outlook with OAuth 2, use auth: SmtpAuth.xoauth2. The username is the email and the password is the access token.

keepAlive: true is good when you send many emails. One connection sends them one by one. When the server closed it, the next send opens a new one.

For local work, Mailpit catches all emails:

'mailpit': SmtpTransport(
  host: 'localhost',
  port: 1025,
  encryption: SmtpEncryption.none,
),

Amazon SES

There are two classes. Both send the same MIME message, with attachments and inline images.

• SesTransport: SES API v1, SendRawEmail.
• SesV2Transport: SES API v2, SendEmail with raw content.

'ses': SesV2Transport(
  key: Env.get('AWS_ACCESS_KEY_ID'),
  secret: Env.get('AWS_SECRET_ACCESS_KEY'),
  region: Env.get('AWS_REGION', 'us-east-1'),
),

Option	Default	What it does
key	required	the AWS access key id
secret	required	the AWS secret access key
sessionToken	none	for temporary keys, eg. from a role
region	us-east-1	the AWS region of SES
configurationSet	none	the SES configuration set, to track events
endpoint	https://email.<region>.amazonaws.com/	another API address, eg. a VPC endpoint or LocalStack

The requests are signed with AWS Signature Version 4. No AWS SDK is needed.

Azure Communication Services

'azure': AzureTransport(
  endpoint: 'https://my-app.europe.communication.azure.com',
  accessKey: Env.get('AZURE_EMAIL_KEY'),
),

Or with the connection string of the Azure portal:

'azure': AzureTransport.fromConnectionString(
  Env.get('AZURE_EMAIL_CONNECTION_STRING'),
),

Option	Default	What it does
endpoint	required	the address of your resource
accessKey	required	the access key of the resource
apiVersion	2023-03-31	the API version
disableTracking	false	turn off open and click tracking

Requests are signed with the access key (HMAC-SHA256). Inline images need a newer apiVersion that supports them.

Resend

'resend': ResendTransport(apiKey: Env.get('RESEND_API_KEY')),

Mailgun

'mailgun': MailgunTransport(
  apiKey: Env.get('MAILGUN_API_KEY'),
  domain: 'mg.example.com',
  region: MailgunRegion.eu,
),

region is MailgunRegion.us (the default) or MailgunRegion.eu. Use the region of your Mailgun domain.

Postmark

'postmark': PostmarkTransport(
  serverToken: Env.get('POSTMARK_TOKEN'),
  messageStream: 'outbound',
),

messageStream is optional. Without it, Postmark uses the default stream of the server.

sendmail

Sends with the sendmail program of the server (Postfix, Exim, msmtp and others).

'sendmail': SendmailTransport(
  path: '/usr/sbin/sendmail',
  mode: SendmailMode.smtp,
),

Mode	Command	How it works
SendmailMode.smtp (default)	sendmail -bs	speaks SMTP on stdin and stdout
SendmailMode.pipe	sendmail -t -i	pipes the message in. sendmail reads the recipients from the headers

Log

Prints each email and sends nothing. Good for local work.

'log': LogTransport(),

Pass output to print somewhere else, eg. LogTransport(output: logger.info).

Array

Keeps each email in a list and sends nothing. See Testing.

'array': ArrayTransport(),

Failover

Tries each transport in order, until one sends the email.

SesV2Transport ses = SesV2Transport(key: '...', secret: '...');
SmtpTransport smtp = SmtpTransport(host: 'smtp.example.com');

MailConfig mailConfig = MailConfig(
  defaultMailer: 'main',
  mailers: <String, Transport>{
    'main': FailoverTransport(<Transport>[ses, smtp]),
  },
);

Tags and metadata

Each provider has its own way to group and mark emails. This is what each transport does with tags and metadata:

Transport	tags	metadata
SES	not used	message tags
Resend	tags with the value true	tags
Mailgun	o:tag	variables (v:name)
Postmark	the first tag	metadata
Azure, SMTP, sendmail	not used	not used

For SMTP and sendmail, use headers instead.

Testing

Mail.fake() sends every mailer to one ArrayTransport. Nothing goes out. Then check what was sent.

import 'package:dox_mailer/dox_mailer.dart';
import 'package:test/test.dart';

void main() {
  late ArrayTransport mail;

  setUp(() {
    mail = Mail.fake();
  });

  tearDown(() {
    Mail.restore();
  });

  test('sign up sends a welcome email', () async {
    await signUp('[e-mail]');

    expect(mail.messages, hasLength(1));
    Message message = mail.messages.single;
    expect(message.to.single.email, '[e-mail]');
    expect(message.subject, 'Welcome');
  });
}

Mail.fake() works with or without a config. Call it after the app has started, because MailProvider sets up the config again at start.

mail.clear() forgets the sent emails.

Integration tests

These tests send real email to free test servers and read it back. They are in test/integration/ and have the integration tag. With no servers, dart test skips them.

You need Docker. This starts the servers from docker-compose.yaml and runs the tests:

tool/integration_test.sh

Server	Tests
Mailpit	SMTP: no TLS, STARTTLS, TLS, AUTH PLAIN and LOGIN, keepAlive. sendmail -t -i and -bs
LocalStack	SES v1
moto	SES v1 and v2
api.postmarkapp.com	Postmark, with the test token POSTMARK_API_TEST

The servers keep running. Stop them with docker compose down.

Your own transport

Extend Transport and add it to mailers:

class MyApiTransport extends Transport {
  @override
  Future<SentMessage> send(Message message) async {
    // call your API here
    return SentMessage(message, messageId: 'id from the API');
  }
}

The message is checked, and has a from address, when it gets to send().

For a provider that takes raw MIME, MimeBuilder().build(message) gives the MIME text.