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Email delivery for asyncio.

Project description

Mailers for asyncio

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  • 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.
  • message preprocessors
  • 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[aiosmtplib]

Then create mailer:

from mailers import Mailer

mailer = Mailer("smtp://user:password@localhost:25?timeout=2")
await mailer.send_message(
    to="user@localhost", from_address="from@localhost", subject="Hello", text="World!"

Compose messages

If you need more control over the message, you can use Email object to construct email message and then send it using mailer.send method.

from mailers import Email, Mailer

message = Email(
    text="Hello world!",
    html="<b>Hello world!</b>",
mailer = Mailer("smtp://")
await mailer.send(message)

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 Jinja templates

Requires jinja2 package installed

You can use Jinja to render templates. This way, your text and html can be rendered from a template.

Use TemplatedMailer instead of default Mailer and set a jinja2.Environment instance. Then, call send_templated_message.

import jinja2

from mailers import TemplatedMailer

env = jinja2.Environment(loader=jinja2.FileSystemLoader(["templates"]))
mailer = TemplatedMailer("smtp://", env)
    template_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 file 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)

DKIM signing

Requires dkimpy package installed

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 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 = 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

Use MultiTransport to provide a fallback transport. By default, the first transport is used but if it fails to send the message, it will retry sending using next configured transport.

from mailers import Mailer, MultiTransport, SMTPTransport

primary_transport = SMTPTransport()
fallback_transport = SMTPTransport()

mailer = Mailer(MultiTransport([primary_transport, fallback_transport]))


Preprocessors are function that mailer calls before sending. Preprocessors are simple functions that modify message contents.

Below you see an example preprocessor:

from email.message import EmailMessage

from mailers import Mailer

def attach_html_preprocessor(message: EmailMessage) -> EmailMessage:
    message.add_alternative(b"This is HTML body", subtype="html", charset="utf-8")
    return message

mailer = Mailer(preprocessors=[attach_html_preprocessor])

CSS inliner

Requires toronado package installed

Out of the box we provide mailers.preprocessors.css_inliner utility that converts CSS classes into inline styles.


SMTP transport

Requires aiosmtplib package installed

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

Multi transport

The purpose of this transport is to provide a developer an option to provide a fallback transport. You can configure several channels and MultiTransport will guarantee that at least one will deliver the message.

Class: mailers.transports.MultiTransport DSN: - Options:

  • transports (list[Transport]) - subtransports

Custom transports.

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

from email.message import Message
from mailers import Mailer, Transport

class PrintTransport(Transport):
    async def send(self, message: Message) -> None:

mailer = Mailer(PrintTransport())

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