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Email delivery for asyncio.

Project description

Mailers for asyncio

PyPI GitHub Workflow Status GitHub dependency status for latest release PyPI - Downloads GitHub Release Date Lines of code


  • fully typed
  • full utf-8 support
  • async and sync sending
  • pluggable transports
  • multiple built-in transports including: SMTP, file, null, in-memory, streaming, and console.
  • plugin system
  • embeddables
  • attachments (with async and sync interfaces)
  • message signing via Signer interface (DKIM bundled)
  • message encryption via Encrypter interface
  • trio support via anyio
  • fallback transports
  • global From address
  • templated emails


pip install mailers
from mailers import create_mailer, Email

message = Email(to='user@localhost', from_address='from@localhost', subject='Hello', text='World!')
mailer = create_mailer('smtp://user:password@localhost:25?timeout=2')
await mailer.send(message)

You can also send to multiple recipients by passing an iterable int to argument:

message = Email(to=['user@localhost', 'user2@localhost', 'user@localhost'], ...)

also you can change addresses any time you want:'', '')

same rule applies to to, from_address, cc, bcc, reply_to fields.

Compose messages

The arguments and methods of Email class are self-explanatory so here is an kick-start example:

from mailers import Email

message = Email(
    text='Hello world!',
    html='<b>Hello world!</b>',

cc, bcc, to, reply_to can be either strings or lists of strings.

Global From address

Instead of setting "From" header in every message, you can set it mailer-wide. Use from_address argument of Mailer class:

mailer = Mailer(from_address="sender@localhost")

The mailer will set From header with the given value to all messages that do not container From or Sender headers.

Using templates

You can use any template engine with a special email class called TemplatedEmail. This class extends Email with following arguments:

  • html_template - a template for use in HTML part
  • text_template - a template for use in text part
  • context - a template context

Then, you need to use appropriate plugin that can render the email message.

Out of the box, we provide a Jinja adapter.

Use Jinja2 engine

You can use Jinja template engine to render your emails. Add JinjaRendererPlugin with a preconfigured jinja2.Environment instance. Then, use mailers.TemplatedEmail instead of mailers.Email to configure templated mail.

import jinja2

from mailers import Mailer, TemplatedEmail
from mailers.plugins.jinja_renderer import JinjaRendererPlugin

env = jinja2.Environment(loader=jinja2.FileSystemLoader(['templates']))
mailer = Mailer(plugins=[JinjaRendererPlugin])

email = TemplatedEmail(subject='Hello', text_template='mail.txt', html_template='mail.html', context={'user': 'root'})


Use attach, attach_from_path, attach_from_path_sync methods to attach files.

from mailers import Email

message = Email(to='user@localhost', from_address='from@example.tld', text='Hello world!')

# attachments can be added on demand
await message.attach_from_path('file.txt')

# or use blocking sync version

# attach from variable
message.attach('CONTENTS', 'file.txt', 'text/plain')

Embedding files

In the same way as with attachments, you can inline files into your messages. This is commonly used to display embedded images in the HTML body. Here are method you can use embed, embed_from_path, embed_from_path_sync.

from mailers import Email

message = Email(
    html='Render me <img src="cid:img1">',

await message.embed_from_path(path='/path/to/image.png', name='img1')

Note, that you have to add HTML part to embed files. Otherwise, they will be ignored.

Message signatures

You can sign messages (e.g. with DKIM) by passing signer argument to the Mailer instance.

signer = MySigner()
mailer = Mailer(..., signer=signer)

# or
mailer = create_mailer(..., signer=signer)

DKIM signing

You may wish to add DKIM signature to your messages to prevent them from being put into the spam folder.

Note, you need to install dkimpy package before using this feature.

from mailers import create_mailer
from mailers.signers.dkim import DKIMSigner

signer = DKIMSigner(selector='default', private_key_path='/path/to/key.pem')

# or you can put key content using private_key argument
signer = DKIMSigner(selector='default', private_key='PRIVATE KEY GOES here...')

mailer = create_mailer('smtp://', signer=signer)

Now all outgoing messages will be signed with DKIM method.

The plugin signs "From", "To", "Subject" headers by default. Use "headers" argument to override it.

Custom signers

Extend mailers.Signer class and implement sign method:

from email.message import Message
from mailers import Signer

class MySigner(Signer):
    def sign(self, message: Message) -> Message:
        # message signing code here...
        return message


When encrypting a message, the entire message (including attachments) is encrypted using a certificate. Therefore, only the recipients that have the corresponding private key can read the original message contents.

encrypter = MyEncrypter()
mailer = Mailer(..., encrypter=encrypter)

Now all message content will be encrypted.

Custom encrypters

Extend mailers.Encrypter class and implement encrypt method:

from email.message import Message
from mailers import Encrypter

class MyEncrypter(Encrypter):
    def encrypt(self, message: Message) -> Message:
        # message encrypting code here...
        return message

High Availability

You can pass multiples transports to the Mailer instance and it will iterate over them asking each to send a message. By default, the first transport is used but if it fails to send the message, the mailer will retry sending with the next transport in the chain.

mailer = Mailer([transport1, transport2, ..., transportN])


Plugins let you inspect and modify outgoing messages before or after they are sent. The plugin is a class that implements mailers.plugins.Plugin protocol. Plugins are added to mailers via plugins argument.

Below you see an example plugin:

from email.message import Message

from mailers import BasePlugin, create_mailer, Mailer, SentMessages

class PrintPlugin(BasePlugin):

    async def on_before_send(self, message: Message) -> None:
        print('sending message %s.' % message)

    async def on_after_send(self, message: Message, sent_messages: SentMessages) -> None:
        print('message has been sent %s.' % message)

    async def on_send_error(self, message: Message, sent_messages: SentMessages) -> None:
        print('error sending message %s.' % message)

mailer = Mailer(plugins=[PrintPlugin()])

# or if you use create_mailer shortcut
mailer = create_mailer(plugins=[PrintPlugin()])


SMTP transport

Send messages via third-party SMTP servers.

Class: mailers.transports.SMTPTransport directory smtp://user:pass@hostname:port?timeout=&use_tls=1 Options:

  • host (string, default "localhost") - SMTP server host
  • port (string, default "25") - SMTP server port
  • user (string) - SMTP server login
  • password (string) - SMTP server login password
  • use_tls (string, choices: "yes", "1", "on", "true") - use TLS
  • timeout (int) - connection timeout
  • cert_file (string) - path to certificate file
  • key_file (string) - path to key file

File transport

Write outgoing messages into a directory in EML format.

Class: mailers.transports.FileTransport DSN: file:///tmp/mails Options:

  • directory (string) path to a directory

Null transport

Discards outgoing messages. Takes no action on send.

Class: mailers.transports.NullTransport DSN: null://

Memory transport

Keeps all outgoing messages in memory. Good for testing.

Class: mailers.transports.InMemoryTransport DSN: memory:// Options:

  • storage (list of strings) - outgoing message container

You can access the mailbox via ".mailbox" attribute.


from mailers import Mailer, InMemoryTransport, Email

transport = InMemoryTransport([])
mailer = Mailer(transport)

await mailer.send(Email(...))
assert len(transport.mailbox) == 1  # here are all outgoing messages

Streaming transport

Writes all messages into a writable stream. Ok for local development.

Class: mailers.transports.StreamTransport DSN: unsupported Options:

  • output (typing.IO) - a writable stream


import io
from mailers import Mailer, StreamTransport

transport = StreamTransport(output=io.StringIO())
mailer = Mailer(transport)

Console transport

This is a preconfigured subclass of streaming transport. Writes to sys.stderr by default.

Class: mailers.transports.ConsoleTransport DSN: console:// Options:

  • output (typing.IO) - a writeable stream

Custom transports.

Each transport must extend mailers.transports.Transport base class.

import typing as t
from email.message import Message
from mailers import Mailer, Transport, EmailURL, SentMessage

class PrintTransport(Transport):
    def from_url(cls, url: t.Union[str, EmailURL]) -> t.Optional[Transport]:
        # this method is optional,
        # if your transport does not support instantiation from URL then return None here.
        # returning None is the default behavior
        return None

    async def send(self, message: Message) -> SentMessage:
        return SentMessage(True, message, self)

mailer = Mailer(PrintTransport())

The library will call Transport.from_url when it needs to instantiate the transport instance from the URL. It is ok to return None as call result then the transport will be instantiated using construction without any arguments passed.

Once you have defined a new transport, register a URL protocol for it:

add_protocol_handler('print', PrintTransport)
mailer = Mailer('print://')

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