Programmatic usage
If you already have an asyncio event loop, you can create a server using
the SMTP
class as the protocol factory, and then run the loop forever.
If you need to pass arguments to the SMTP
constructor, use
functools.partial()
or write your own wrapper function. You might also
want to add a signal handler so that the loop can be stopped, say when you hit
control-C.
It’s probably easier to use a threaded controller which runs the SMTP server in a
separate thread with a dedicated event loop. The controller provides useful
and reliable start
and stop
semantics so that the foreground thread
doesn’t block. Among other use cases, this makes it convenient to spin up an
SMTP server for unit tests.
In both cases, you need to pass a handler to the SMTP
constructor. Handlers respond to events that you care about during the SMTP
dialog.
Important
Consider running the controller in a separate Python process (e.g., using the
multiprocessing
module) if you don’t want your main Python process to be
blocked when aiosmtpd is handling extra-large emails.
Using the controller
TCP-based Server
The Controller
class creates a TCP-based server,
listening on an Internet endpoint (i.e., ip_address:port
pair).
Say you want to receive email for example.com
and print incoming mail data
to the console. Start by implementing a handler as follows:
>>> import asyncio
>>> class ExampleHandler:
... async def handle_RCPT(self, server, session, envelope, address, rcpt_options):
... if not address.endswith('@example.com'):
... return '550 not relaying to that domain'
... envelope.rcpt_tos.append(address)
... return '250 OK'
...
... async def handle_DATA(self, server, session, envelope):
... print('Message from %s' % envelope.mail_from)
... print('Message for %s' % envelope.rcpt_tos)
... print('Message data:\n')
... for ln in envelope.content.decode('utf8', errors='replace').splitlines():
... print(f'> {ln}'.strip())
... print()
... print('End of message')
... return '250 Message accepted for delivery'
Pass an instance of your ExampleHandler
class to the Controller
, and
then start it:
>>> from aiosmtpd.controller import Controller
>>> controller = Controller(ExampleHandler())
>>> controller.start()
The SMTP thread might run into errors during its setup phase; to catch this
the main thread will timeout when waiting for the SMTP server to become ready.
By default the timeout is set to 1 second but can be changed either by using
the AIOSMTPD_CONTROLLER_TIMEOUT
environment variable or by passing a
different ready_timeout
duration to the Controller’s constructor.
Connect to the server and send a message, which then gets printed by
ExampleHandler
:
>>> from smtplib import SMTP as Client
>>> client = Client(controller.hostname, controller.port)
>>> r = client.sendmail('a@example.com', ['b@example.com'], """\
... From: Anne Person <anne@example.com>
... To: Bart Person <bart@example.com>
... Subject: A test
... Message-ID: <ant>
...
... Hi Bart, this is Anne.
... """)
Message from a@example.com
Message for ['b@example.com']
Message data:
> From: Anne Person <anne@example.com>
> To: Bart Person <bart@example.com>
> Subject: A test
> Message-ID: <ant>
>
> Hi Bart, this is Anne.
End of message
You’ll notice that at the end of the DATA
command, your handler’s
handle_DATA()
method was called. The sender, recipients, and message
contents were taken from the envelope, and printed at the console. The
handler methods also returns a successful status message.
The ExampleHandler
class also implements a handle_RCPT()
method. This
gets called after the RCPT TO
command is sanity checked. The method
ensures that all recipients are local to the @example.com
domain,
returning an error status if not. It is the handler’s responsibility to add
valid recipients to the rcpt_tos
attribute of the envelope and to return a
successful status.
Thus, if we try to send a message to a recipient not inside example.com
,
it is rejected:
>>> client.sendmail('aperson@example.com', ['cperson@example.net'], """\
... From: Anne Person <anne@example.com>
... To: Chris Person <chris@example.net>
... Subject: Another test
... Message-ID: <another>
...
... Hi Chris, this is Anne.
... """)
Traceback (most recent call last):
...
smtplib.SMTPRecipientsRefused: {'cperson@example.net': (550, b'not relaying to that domain')}
When you’re done with the SMTP server, stop it via the controller.
>>> controller.stop()
The server is guaranteed to be stopped.
>>> client.connect(controller.hostname, controller.port)
Traceback (most recent call last):
...
ConnectionRefusedError: ...
There are a number of built-in handler classes that you can use to do some common tasks, and it’s easy to write your own handler. For a full overview of the methods that handler classes may implement, see the section on handler hooks.
Unix Socket-based Server
The UnixSocketController
class creates a server listening to
a Unix Socket (i.e., a special file that can act as a ‘pipe’ for interprocess
communication).
Usage is identical with the example described in the TCP-based Server section above, with some differences:
Rather than specifying a hostname:port to listen on, you specify the Socket’s filepath:
>>> from aiosmtpd.controller import UnixSocketController
>>> from aiosmtpd.handlers import Sink
>>> controller = UnixSocketController(Sink(), unix_socket="smtp_socket~")
>>> controller.start()
Warning
Do not exceed the Operating System limit for the length of the socket file path. On Linux, the limit is 108 characters. On BSD OSes, it’s 104 characters.
Rather than connecting to IP:port, you connect to the Socket file.
Python’s smtplib.SMTP
class sadly cannot connect to a Unix Socket,
so we need to handle it on our own here:
>>> import socket
>>> sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
>>> sock.connect("smtp_socket~")
>>> sock.recv(1024)
b'220 ...'
Try sending something, don’t forget to end with "\r\n"
:
>>> sock.send(b"HELO example.org\r\n")
18
>>> sock.recv(1024)
b'250 ...'
And close everything when done:
>>> sock.send(b"QUIT\r\n")
6
>>> sock.recv(1024)
b'221 Bye...'
>>> sock.close()
>>> controller.stop()
Unthreaded Controllers
In addition to the threaded controllers described above,
aiosmtpd
also provides the following UNthreaded controllers:
UnthreadedController
– the unthreaded version ofController
UnixSocketUnthreadedController
– the unthreaded version ofUnixSocketController
These classes are considered advanced classes, because you’ll have to manage the event loop yourself.
For example, to start an unthreaded controller, you’ll have to do something similar to this:
>>> import asyncio
>>> loop = asyncio.new_event_loop()
>>> asyncio.set_event_loop(loop)
>>> from aiosmtpd.controller import UnthreadedController
>>> from aiosmtpd.handlers import Sink
>>> controller = UnthreadedController(Sink(), loop=loop)
>>> controller.begin()
Note that unlike the threaded counterparts,
the method used to start the controller is named begin()
.
And unlike the method in the threaded version,
begin()
does NOT start the asyncio event loop;
you’ll have to start it yourself.
For the purposes of trying this, let’s create a thread and have it run the asyncio event loop; we’ll also schedule an autostop so it won’t hang:
>>> def runner():
... # Set the delay to something long enough so you have time
... # to do some testing
... loop.call_later(3.0, loop.stop)
... loop.run_forever()
>>> import threading
>>> thread = threading.Thread(target=runner)
>>> thread.daemon = True
>>> thread.start()
>>> import time
>>> time.sleep(0.1) # Allow the loop to begin
At this point in time, the server would be listening:
>>> from smtplib import SMTP as Client
>>> client = Client(controller.hostname, controller.port)
>>> client.helo("example.com")
(250, ...)
>>> client.quit()
(221, b'Bye')
The complex thing will be to end it; that is why we’re marking these classes as “advanced”.
For our example here, since we have created an “autostop loop”, all we have to do is wait for the runner thread to end:
>>> thread.join()
>>> loop.is_running()
False
We still need to do some cleanup to fully release the bound port.
Since the loop has ended, we can simply call the end()
method:
>>> controller.end()
If you want to end the controller but keep the loop running, you’ll have to do it like this:
loop.call_soon_threadsafe(controller.end)
# If you want to ensure that controller has stopped, you can wait() here:
controller.ended.wait(10.0) # Optional
You must remember to cleanup the canceled tasks yourself.
We have provided a convenience method,
cancel_tasks()
:
# Will also stop the loop!
loop.call_soon_threadsafe(controller.cancel_tasks)
(If you invoke cancel_tasks
with the parameter stop_loop=False
,
then loop will NOT be stopped.
That is a much too-advanced topic and we will not discuss it further in this documentation.)
The Unix Socket variant, UnixSocketUnthreadedController
, works in the same way.
The difference is only in how to access the server, i.e., through a Unix Socket instead of TCP/IP.
We’ll leave out the details for you to figure it out yourself.
Enabling SMTPUTF8
It’s very common to want to enable the SMTPUTF8
ESMTP option, therefore
this is the default for the Controller
constructor. For backward
compatibility reasons, this is not the default for the SMTP
class
though. If you want to disable this in the Controller
, you can pass this
argument into the constructor:
>>> from aiosmtpd.handlers import Sink
>>> controller = Controller(Sink(), enable_SMTPUTF8=False)
>>> controller.start()
>>>
>>> client = Client(controller.hostname, controller.port)
>>> code, message = client.ehlo('me')
>>> code
250
The EHLO response does not include the SMTPUTF8
ESMTP option.
>>> lines = message.decode('utf-8').splitlines()
>>> # Don't print the server host name line, since that's variable.
>>> for line in lines[1:]:
... print(line)
SIZE 33554432
8BITMIME
HELP
Stop the controller if we’re done experimenting:
>>> controller.stop()
Controller API
- aiosmtpd.controller.get_localhost()
- Returns:
The numeric address of the loopback interface;
"::1"
if IPv6 is supported,"127.0.0.1"
if IPv6 is not supported.- Return type:
Literal[“::1”, “127.0.0.1”]
- class aiosmtpd.controller.IP6_IS
- NO: set[int]
Contains constants from
errno
that will be raised bysocket.socket.bind()
if IPv6 is NOT available on the system.
- YES: set[int]
Contains constants from
errno
that will be raised bysocket.socket.bind()
if IPv6 IS available on the system.
Note
You can customize the contents of these attributes by adding/removing from them, in case the behavior does not align with your expectations and you cannot wait for a patch to be merged.
- class aiosmtpd.controller.BaseController(handler, loop=None, *, ssl_context=None, server_hostname=None, server_kwargs=None, **SMTP_parameters)
This Abstract Base Class defines parameters, attributes, and methods common between all concrete controller classes.
- Parameters:
handler – Handler object
loop (asyncio.AbstractEventLoop) – The asyncio event loop in which the server will run. If not given,
asyncio.new_event_loop()
will be called to create the event loop.ssl_context (ssl.SSLContext) – SSL Context to wrap the socket in. Will be passed-through to
create_server()
methodserver_hostname (Optional[str]) – Server’s hostname, will be passed-through as
hostname
parameter ofSMTP
server_kwargs (dict) – (DEPRECATED) A dict that will be passed-through as keyword arguments of
SMTP
. This is DEPRECATED; please use**SMTP_parameters
instead.SMTP_parameters – Optional keyword arguments that will be passed-through as keyword arguments of
SMTP
Attributes- handler
The instance of the event handler passed to the constructor.
- loop
The event loop being used.
- server
This is the server instance returned by
_create_server()
after the server has started.You can retrieve the
socket
objects the server is listening on from theserver.sockets
attribute.
- smtpd: aiosmtpd.smtp.SMTP
The server instance (of class SMTP) created by
factory()
after the controller is started.
Methods- factory() aiosmtpd.smtp.SMTP
You can override this method to create custom instances of the
SMTP
class being controlled.By default, this creates an
SMTP
instance, passing in your handler and setting flags from the**SMTP_Parameters
parameter.Examples of why you would want to override this method include creating an LMTP server instance instead of the standard
SMTP
server.
- class aiosmtpd.controller.Controller(handler, hostname=None, port=8025, loop=None, *, ready_timeout=DEFAULT_READY_TIMEOUT, ssl_context=None, server_hostname=None, server_kwargs=None, **SMTP_parameters)
A concrete subclass of
BaseController
that provides a threaded, INET listener.- Parameters:
hostname (Optional[str]) – Will be given to the event loop’s
create_server()
method as thehost
parameter, with a slight processing (see below)port (int) – Will be passed-through to
create_server()
methodready_timeout (float) – How long to wait until server starts. The
AIOSMTPD_CONTROLLER_TIMEOUT
takes precedence over this parameter. Seeready_timeout
for more information.
Other parameters are defined in the
BaseController
class.The
hostname
parameter will be passed to the event loop’screate_server()
method as thehost
parameter, exceptNone
(default) will be translated to::1
.To bind dual-stack locally, use
localhost
.To bind dual-stack on all interfaces, use
""
(empty string).
Important
The
hostname
parameter does NOT get passed through to the SMTP instance; if you want to give the SMTP instance a custom hostname (e.g., for use in HELO/EHLO greeting), you must pass it through theserver_hostname
parameter.Explicitly defined SMTP keyword arguments will override keyword arguments of the same names defined in the (deprecated)
server_kwargs
argument.>>> from aiosmtpd.controller import Controller >>> from aiosmtpd.handlers import Sink >>> controller = Controller( ... Sink(), timeout=200, server_kwargs=dict(timeout=400) ... ) >>> controller.SMTP_kwargs["timeout"] 200
Finally, setting the
ssl_context
parameter will switch the protocol toSMTPS
mode, implying unconditional encryption of the connection, and preventing the use of theSTARTTLS
mechanism.Actual behavior depends on the subclass’s implementation.
AttributesIn addition to those provided by
BaseController
, this class provides the following:- hostname: str
- port: int
The values of the hostname and port arguments.
- ready_timeout: float
The timeout value used to wait for the server to start.
This will either be the value of the
AIOSMTPD_CONTROLLER_TIMEOUT
environment variable (converted to float), or theready_timeout
parameter.Setting this to a high value will NOT slow down controller startup, because it’s a timeout limit rather than a sleep delay. However, you may want to reduce the default value to something ‘just enough’ so you don’t have to wait too long for an exception, if problem arises.
If this timeout is breached, a
TimeoutError
exception will be raised.
MethodsIn addition to those provided by
BaseController
, this class provides the following:- start() None
- Raises:
TimeoutError – if the server takes too long to get ready, exceeding the
ready_timeout
parameter.RuntimeError – if an unrecognized & unhandled error happened, resulting in non-creation of a server object (
smtpd
remainsNone
)
Start the server in the subthread. The subthread is always a
daemon thread
(i.e., we always setthread.daemon=True
).Exceptions can be raised if the server does not start within
ready_timeout
seconds, or if any other exception occurs infactory()
while creating the server.Important
If
start()
raises an Exception, cleanup is not performed automatically, to support deep inspection post-exception (if you wish to do so.) Cleanup must still be performed manually by callingstop()
For example:
# Assume SomeController is a concrete subclass of BaseThreadedController controller = SomeController(handler) try: controller.start() except ...: ... exception handling and/or inspection ... finally: controller.stop()
- stop(no_assert=False) None
- Parameters:
no_assert (bool) – If
True
, skip the assertion step so anAssertionError
will not be raised if thread had not been started successfully.- Raises:
AssertionError – if this method is called before
start()
is called successfully ANDno_assert=False
Stop the server and the event loop, and cancel all tasks via
cancel_tasks()
.
- class aiosmtpd.controller.UnixSocketController(handler, unix_socket, loop=None, *, ready_timeout=DEFAULT_READY_TIMEOUT, ssl_context=None, server_hostname=None, **SMTP_parameters)
A concrete subclass of
BaseController
that provides a threaded, Unix Socket listener.- Parameters:
unix_socket (Union[str, pathlib.Path]) – Socket file, will be passed-through to
asyncio.loop.create_unix_server()
For the other parameters, see the description under
Controller
AttributesOther attributes (except
hostname
andport
) are identical toController
and thus are not repeated nor explained here.MethodsAll methods are identical to
Controller
and thus are not repeated nor explained here.
- class aiosmtpd.controller.UnthreadedController(handler, hostname=None, port=8025, loop=None, *, ssl_context=None, server_hostname=None, server_kwargs=None, **SMTP_parameters)
Added in version 1.5.0.
A concrete subclass of
BaseController
that provides an UNthreaded, INET listener.Parameters are identical to the
Controller
class.AttributesAttributes are identical to the
Controller
class with one addition:- ended: threading.Event
An
Event
that can be.wait()
-ed when ending the controller. Please see the Unthreaded Controllers section for more info.
MethodsIn addition to those provided by
BaseController
, this class provides the following:- begin()
Initializes the server task and insert it into the asyncio event loop.
Note
The SMTP class itself will only be initialized upon first connection to the server task.
- async finalize()
Perform orderly closing of the server listener. If you need to close the server from a non-async function, you can use the
end()
method instead.Upon completion of this method, the
ended
attribute will beset()
.
- end()
This is a convenience method that will asynchronously invoke the
finalize()
method. This method non-async, and thus is callable from non-async functions.Note
If the asyncio event loop has been stopped, then it is safe to invoke this method directly. Otherwise, it is recommended to invoke this method using the
call_soon_threadsafe()
method.
- class aiosmtpd.controller.UnixSocketUnthreadedController(handler, unix_socket, loop=None, *, ssl_context=None, server_hostname=None, server_kwargs=None, **SMTP_parameters)
Added in version 1.5.0.
A concrete subclass of
BaseController
that provides an UNthreaded, Unix Socket listener.Parameters are identical to the
UnixSocketController
class.AttributesAttributes are identical to the
UnixSocketController
class, with the following addition:- ended: threading.Event
An
Event
that can be.wait()
-ed when ending the controller. Please see the Unthreaded Controllers section for more info.
MethodsMethods are identical to the
UnthreadedController
class.