Litestar Email

litestar-email

litestar-email 0.4.0 provides one async sending interface for console, memory, SMTP, Resend, SendGrid, Mailgun, Amazon SES, and custom backends. Match the backend already selected by the project; keep message construction independent from the transport.

Code Style Rules

• Use NamedDependency[EmailService] for handler injection. The plugin registers a named Litestar dependency, not a global service singleton.
• Pass recipient collections as list[str]. to, cc, bcc, and reply_to are list fields.
• Pass attachment content as bytes. Do file I/O before constructing the message and keep that I/O async.
• Await send_message() and send_messages(). Both return the count sent.
• Keep API keys and SMTP credentials in the project's settings layer.

Quick Reference

Install

pip install "litestar-email>=0.4.0"
pip install "litestar-email[smtp]>=0.4.0"   # aiosmtplib
pip install "litestar-email[ses]>=0.4.0"    # botocore for SigV4
pip install "litestar-email[httpx]>=0.4.0"   # default HTTP transport
pip install "litestar-email[aiohttp]>=0.4.0" # alternative HTTP transport

The HTTP API backends select httpx by default, but the transport is optional in litestar-email itself. Install the httpx or aiohttp extra (unless the project already provides that dependency), and select aiohttp only when the project standardizes on it.

Configure the Plugin

from os import environ

from litestar import Litestar
from litestar_email import EmailConfig, EmailPlugin, SMTPConfig

email_config = EmailConfig(
    backend=SMTPConfig(
        host="smtp.example.com",
        port=587,
        username=environ["SMTP_USERNAME"],
        password=environ["SMTP_PASSWORD"],
        use_tls=True,
    ),
    from_email="noreply@example.com",
    from_name="Example App",
)

app = Litestar(plugins=[EmailPlugin(config=email_config)])

EmailConfig fields:

The dependency and state keys occupy separate namespaces. Change them independently when the application already uses either key:

email_config = EmailConfig(
    backend="memory",
    email_service_dependency_key="email_service",
    email_service_state_key="email_config",
)

Inject EmailService

The handler parameter name must match email_service_dependency_key:

from litestar import post
from litestar.di import NamedDependency
from litestar_email import EmailMessage, EmailService


@post("/notifications")
async def send_notification(
    mailer: NamedDependency[EmailService],
) -> dict[str, int]:
    sent = await mailer.send_message(
        EmailMessage(
            subject="Notification",
            body="You have a new notification.",
            to=["recipient@example.com"],
        ),
    )
    return {"sent": sent}

EmailPlugin.on_app_init() registers:

• config.provide_service under email_service_dependency_key;
• the public email types in Litestar's signature namespace;
• the EmailConfig instance under email_service_state_key in app state.

App state does not contain a permanently open EmailService. Use plugin.get_service(app.state) or config.get_service(app.state) when code outside handler DI needs a service derived from app state.

Construct Messages

subject and body are required constructor arguments. Recipient lists have empty-list defaults, so provide at least one delivery recipient before sending.

from litestar_email import EmailMessage

message = EmailMessage(
    subject="Monthly report",
    body="The report is attached.",
    from_email="Reports <reports@example.com>",
    to=["owner@example.com"],
    cc=["audit@example.com"],
    bcc=["archive@example.com"],
    reply_to=["support@example.com"],
    headers={"X-Campaign-ID": "monthly-report"},
)
message.attach(
    filename="report.pdf",
    content=b"report content",
    mimetype="application/pdf",
)
message.attach_alternative(
    content="<p>The report is attached.</p>",
    mimetype="text/html",
)

EmailMessage does not accept html_body or from_name. Put a per-message display name in from_email, as shown above. Use EmailMultiAlternatives.html_body for the HTML convenience constructor:

from litestar_email import EmailMultiAlternatives

message = EmailMultiAlternatives(
    subject="Welcome",
    body="Welcome to Example App.",
    to=["user@example.com"],
    html_body="<p>Welcome to <strong>Example App</strong>.</p>",
)

The message collections have these exact shapes:

recipients() returns to + cc + bcc; it does not include reply_to.

Pick a Backend

Backend config fields:

For SMTP, use_tls=True performs STARTTLS after connecting; use_ssl=True uses implicit TLS. Select the mode required by the SMTP server.

For HTTP backends, http_transport accepts "httpx", "aiohttp", or an HTTPTransport class. Keep the default when the project has no transport preference.

Amazon SES Contract

The 0.4.0 SES backend:

• calls the SES API v2 SendEmail endpoint with Simple content;
• signs the exact transmitted JSON bytes with botocore SigV4;
• uses explicit SESConfig credentials when both key fields are set;
• otherwise uses botocore's default credential chain;
• supports text plus the first text/html alternative;
• supports to, cc, bcc, and the complete reply_to list;
• rejects attachments with EmailDeliveryError because Simple content does not support raw MIME attachments;
• rejects messages with neither a non-empty text body nor an HTML alternative;
• always propagates EmailRateLimitError and EmailAuthenticationError, even when fail_silently=True.

Use SMTP or another attachment-capable backend when the message includes files. Do not imply that SES 0.4.0 sends raw MIME content.

Service Lifecycle

from litestar_email import EmailConfig, EmailMessage, SMTPConfig

config = EmailConfig(
    backend=SMTPConfig(host="localhost", port=1025),
    from_email="noreply@example.com",
)

messages = [
    EmailMessage(subject="One", body="First", to=["one@example.com"]),
    EmailMessage(subject="Two", body="Second", to=["two@example.com"]),
]

async with config.provide_service() as mailer:
    sent = await mailer.send_messages(messages)

Outside a service context, each send_message() or send_messages() call creates, opens, and closes a backend. Inside config.provide_service() or async with EmailService(config), calls reuse one open backend until context exit. Litestar DI consumes the provider as an async iterator and performs the same cleanup.

send_messages([]) returns 0. send_message(message) delegates to send_messages([message]) and returns 0 or 1.

Exception Hierarchy

EmailError
├── EmailBackendError
├── EmailDeliveryError
│   ├── EmailConnectionError
│   ├── EmailAuthenticationError
│   └── EmailRateLimitError
└── MissingDependencyError (also inherits ImportError)

EmailRateLimitError.retry_after is int | None. Unknown backend names raise ValueError; missing optional packages raise MissingDependencyError. Catch specific delivery failures before EmailDeliveryError:

from litestar_email import (
    EmailAuthenticationError,
    EmailConnectionError,
    EmailDeliveryError,
    EmailRateLimitError,
)

try:
    await mailer.send_message(message)
except EmailRateLimitError as exc:
    await schedule_retry(delay=exc.retry_after or 60)
except EmailAuthenticationError:
    await alert_operators("Email credentials were rejected")
except EmailConnectionError:
    await schedule_retry(delay=30)
except EmailDeliveryError:
    await record_delivery_failure()

In-Memory Testing

InMemoryBackend.outbox is a class-level list shared by every memory backend instance. Clear it around each test:

from collections.abc import Iterator

import pytest
from litestar_email import EmailConfig, EmailMessage
from litestar_email.backends import InMemoryBackend


@pytest.fixture(autouse=True)
def clear_email_outbox() -> Iterator[None]:
    InMemoryBackend.clear()
    yield
    InMemoryBackend.clear()


@pytest.mark.anyio
async def test_welcome_email() -> None:
    config = EmailConfig(backend="memory", from_email="test@example.com")

    async with config.provide_service() as mailer:
        sent = await mailer.send_message(
            EmailMessage(
                subject="Welcome",
                body="Thanks for signing up.",
                to=["user@example.com"],
            ),
        )

    assert sent == 1
    assert len(InMemoryBackend.outbox) == 1
    assert InMemoryBackend.outbox[0].subject == "Welcome"

For direct backend tests, use backend = config.get_backend() and await backend.send_messages([...]). In-memory inspection uses InMemoryBackend.outbox.

Workflow

1. Inspect the project's existing provider, network policy, and dependency extras. Keep its backend unless the user asks to migrate.
2. Build one EmailConfig with the selected backend config and default sender.
3. Register EmailPlugin(config=...) and inject the configured dependency key with NamedDependency[EmailService].
4. Construct EmailMessage with plain text. Add HTML through attach_alternative() or EmailMultiAlternatives.
5. Load attachment bytes asynchronously, then call attach().
6. Reuse a service context for batches. Let Litestar DI manage request-scoped service cleanup in handlers.
7. Use backend="memory" in tests and clear InMemoryBackend.outbox between tests.
8. For slow or retryable delivery, use the queue system already present in the project. Choose litestar-queues or litestar-saq only when it matches the existing stack.

Guardrails

• Do not pass html_body to EmailMessage; only EmailMultiAlternatives defines that field.
• Do not pass file paths as attachments. Pass (filename, content_bytes, mimetype) or call attach().
• Do not pass a string to reply_to; pass list[str].
• Do not read app state as an open service by default. The plugin stores its EmailConfig there and derives services from it.
• Do not configure a named API backend separately from its settings. Use backend=ResendConfig(...), backend=SendGridConfig(...), backend=MailgunConfig(...), or backend=SESConfig(...).
• Do not send SES attachments. Select an attachment-capable backend.
• Do not assume fail_silently=True suppresses every exception. SES authentication and rate-limit failures always propagate.
• Do not hard-code API keys, SMTP passwords, or AWS credentials.
• Do not force a provider migration. Match the project's deployed backend and operational constraints.

Validation

• litestar-email>=0.4.0 and the selected backend extra are installed.
• EmailPlugin(config=...) is registered.
• The handler name matches email_service_dependency_key.
• Handler injection uses NamedDependency[EmailService].
• EmailMessage supplies subject, body, and a delivery recipient.
• Attachments are byte triples and the selected backend supports them.
• HTML content is stored in alternatives, not passed to EmailMessage.
• SMTP TLS mode matches the server.
• SES messages contain no attachments and contain text or HTML.
• Batch sends reuse a managed service context.
• Tests clear and assert InMemoryBackend.outbox.
• Delivery exceptions are caught from most specific to least specific.
• Secrets come from the project's settings layer.

Example

from dataclasses import dataclass
from html import escape

from litestar import Litestar, post
from litestar.di import NamedDependency
from litestar.params import JSONBody
from litestar_email import (
    EmailConfig,
    EmailMessage,
    EmailPlugin,
    EmailService,
)


@dataclass
class Notification:
    recipient: str
    subject: str
    text: str


@post("/notifications")
async def create_notification(
    data: JSONBody[Notification],
    mailer: NamedDependency[EmailService],
) -> dict[str, int]:
    message = EmailMessage(
        subject=data.subject,
        body=data.text,
        to=[data.recipient],
    )
    message.attach_alternative(
        content=f"<p>{escape(data.text)}</p>",
        mimetype="text/html",
    )
    return {"sent": await mailer.send_message(message)}


email_config = EmailConfig(
    backend="memory",
    from_email="notifications@example.com",
    from_name="Example App",
)

app = Litestar(
    route_handlers=[create_notification],
    plugins=[EmailPlugin(config=email_config)],
)

References Index

• Litestar dependency injection
• Litestar settings
• Litestar Queues
• Litestar SAQ
• Litestar testing

Official References

• PyPI release 0.4.0
• Message API at v0.4.0
• Configuration API at v0.4.0
• Plugin lifecycle at v0.4.0
• Service lifecycle at v0.4.0
• Exception hierarchy at v0.4.0
• SES backend at v0.4.0
• Tagged tests at v0.4.0

Shared Styleguide Baseline

• General Principles
• Python
• Litestar