| Python 3.6.5 Documentation > "smtpd" — SMTP Server
"smtpd" — SMTP Server
*********************
**Source code:** Lib/smtpd.py
======================================================================
This module offers several classes to implement SMTP (email) servers.
See also: The aiosmtpd package is a recommended replacement for this
module. It is based on "asyncio" and provides a more straightforward
API. "smtpd" should be considered deprecated.
Several server implementations are present; one is a generic do-
nothing implementation, which can be overridden, while the other two
offer specific mail-sending strategies.
Additionally the SMTPChannel may be extended to implement very
specific interaction behaviour with SMTP clients.
The code supports **RFC 5321**, plus the **RFC 1870** SIZE and **RFC
6531** SMTPUTF8 extensions.
SMTPServer Objects
==================
class smtpd.SMTPServer(localaddr, remoteaddr, data_size_limit=33554432, map=None, enable_SMTPUTF8=False, decode_data=False)
Create a new "SMTPServer" object, which binds to local address
*localaddr*. It will treat *remoteaddr* as an upstream SMTP
relayer. Both *localaddr* and *remoteaddr* should be a (host,
port) tuple. The object inherits from "asyncore.dispatcher", and
so will insert itself into "asyncore"’s event loop on
instantiation.
*data_size_limit* specifies the maximum number of bytes that will
be accepted in a "DATA" command. A value of "None" or "0" means no
limit.
*map* is the socket map to use for connections (an initially empty
dictionary is a suitable value). If not specified the "asyncore"
global socket map is used.
*enable_SMTPUTF8* determines whether the "SMTPUTF8" extension (as
defined in **RFC 6531**) should be enabled. The default is
"False". When "True", "SMTPUTF8" is accepted as a parameter to the
"MAIL" command and when present is passed to "process_message()" in
the "kwargs['mail_options']" list. *decode_data* and
*enable_SMTPUTF8* cannot be set to "True" at the same time.
*decode_data* specifies whether the data portion of the SMTP
transaction should be decoded using UTF-8. When *decode_data* is
"False" (the default), the server advertises the "8BITMIME"
extension (**RFC 6152**), accepts the "BODY=8BITMIME" parameter to
the "MAIL" command, and when present passes it to
"process_message()" in the "kwargs['mail_options']" list.
*decode_data* and *enable_SMTPUTF8* cannot be set to "True" at the
same time.
process_message(peer, mailfrom, rcpttos, data, **kwargs)
Raise a "NotImplementedError" exception. Override this in
subclasses to do something useful with this message. Whatever
was passed in the constructor as *remoteaddr* will be available
as the "_remoteaddr" attribute. *peer* is the remote host’s
address, *mailfrom* is the envelope originator, *rcpttos* are
the envelope recipients and *data* is a string containing the
contents of the e-mail (which should be in **RFC 5321** format).
If the *decode_data* constructor keyword is set to "True", the
*data* argument will be a unicode string. If it is set to
"False", it will be a bytes object.
*kwargs* is a dictionary containing additional information. It
is empty if "decode_data=True" was given as an init argument,
otherwise it contains the following keys:
*mail_options*:
a list of all received parameters to the "MAIL" command
(the elements are uppercase strings; example:
"['BODY=8BITMIME', 'SMTPUTF8']").
*rcpt_options*:
same as *mail_options* but for the "RCPT" command.
Currently no "RCPT TO" options are supported, so for now
this will always be an empty list.
Implementations of "process_message" should use the "**kwargs"
signature to accept arbitrary keyword arguments, since future
feature enhancements may add keys to the kwargs dictionary.
Return "None" to request a normal "250 Ok" response; otherwise
return the desired response string in **RFC 5321** format.
channel_class
Override this in subclasses to use a custom "SMTPChannel" for
managing SMTP clients.
New in version 3.4: The *map* constructor argument.
Changed in version 3.5: *localaddr* and *remoteaddr* may now
contain IPv6 addresses.
New in version 3.5: The *decode_data* and *enable_SMTPUTF8*
constructor parameters, and the *kwargs* parameter to
"process_message()" when *decode_data* is "False".
Changed in version 3.6: *decode_data* is now "False" by default.
DebuggingServer Objects
=======================
class smtpd.DebuggingServer(localaddr, remoteaddr)
Create a new debugging server. Arguments are as per "SMTPServer".
Messages will be discarded, and printed on stdout.
PureProxy Objects
=================
class smtpd.PureProxy(localaddr, remoteaddr)
Create a new pure proxy server. Arguments are as per "SMTPServer".
Everything will be relayed to *remoteaddr*. Note that running this
has a good chance to make you into an open relay, so please be
careful.
MailmanProxy Objects
====================
class smtpd.MailmanProxy(localaddr, remoteaddr)
Create a new pure proxy server. Arguments are as per "SMTPServer".
Everything will be relayed to *remoteaddr*, unless local mailman
configurations knows about an address, in which case it will be
handled via mailman. Note that running this has a good chance to
make you into an open relay, so please be careful.
SMTPChannel Objects
===================
class smtpd.SMTPChannel(server, conn, addr, data_size_limit=33554432, map=None, enable_SMTPUTF8=False, decode_data=False)
Create a new "SMTPChannel" object which manages the communication
between the server and a single SMTP client.
*conn* and *addr* are as per the instance variables described
below.
*data_size_limit* specifies the maximum number of bytes that will
be accepted in a "DATA" command. A value of "None" or "0" means no
limit.
*enable_SMTPUTF8* determines whether the "SMTPUTF8" extension (as
defined in **RFC 6531**) should be enabled. The default is
"False". *decode_data* and *enable_SMTPUTF8* cannot be set to
"True" at the same time.
A dictionary can be specified in *map* to avoid using a global
socket map.
*decode_data* specifies whether the data portion of the SMTP
transaction should be decoded using UTF-8. The default is "False".
*decode_data* and *enable_SMTPUTF8* cannot be set to "True" at the
same time.
To use a custom SMTPChannel implementation you need to override the
"SMTPServer.channel_class" of your "SMTPServer".
Changed in version 3.5: The *decode_data* and *enable_SMTPUTF8*
parameters were added.
Changed in version 3.6: *decode_data* is now "False" by default.
The "SMTPChannel" has the following instance variables:
smtp_server
Holds the "SMTPServer" that spawned this channel.
conn
Holds the socket object connecting to the client.
addr
Holds the address of the client, the second value returned by
"socket.accept"
received_lines
Holds a list of the line strings (decoded using UTF-8) received
from the client. The lines have their ""\r\n"" line ending
translated to ""\n"".
smtp_state
Holds the current state of the channel. This will be either
"COMMAND" initially and then "DATA" after the client sends a
“DATA” line.
seen_greeting
Holds a string containing the greeting sent by the client in its
“HELO”.
mailfrom
Holds a string containing the address identified in the “MAIL
FROM:” line from the client.
rcpttos
Holds a list of strings containing the addresses identified in
the “RCPT TO:” lines from the client.
received_data
Holds a string containing all of the data sent by the client
during the DATA state, up to but not including the terminating
""\r\n.\r\n"".
fqdn
Holds the fully-qualified domain name of the server as returned
by "socket.getfqdn()".
peer
Holds the name of the client peer as returned by
"conn.getpeername()" where "conn" is "conn".
The "SMTPChannel" operates by invoking methods named
"smtp_<command>" upon reception of a command line from the client.
Built into the base "SMTPChannel" class are methods for handling
the following commands (and responding to them appropriately):
+----------+---------------------------------------------------------------------+
| Command | Action taken |
+==========+=====================================================================+
| HELO | Accepts the greeting from the client and stores it in |
| | "seen_greeting". Sets server to base command mode. |
+----------+---------------------------------------------------------------------+
| EHLO | Accepts the greeting from the client and stores it in |
| | "seen_greeting". Sets server to extended command mode. |
+----------+---------------------------------------------------------------------+
| NOOP | Takes no action. |
+----------+---------------------------------------------------------------------+
| QUIT | Closes the connection cleanly. |
+----------+---------------------------------------------------------------------+
| MAIL | Accepts the “MAIL FROM:” syntax and stores the supplied address as |
| | "mailfrom". In extended command mode, accepts the **RFC 1870** |
| | SIZE attribute and responds appropriately based on the value of |
| | *data_size_limit*. |
+----------+---------------------------------------------------------------------+
| RCPT | Accepts the “RCPT TO:” syntax and stores the supplied addresses in |
| | the "rcpttos" list. |
+----------+---------------------------------------------------------------------+
| RSET | Resets the "mailfrom", "rcpttos", and "received_data", but not the |
| | greeting. |
+----------+---------------------------------------------------------------------+
| DATA | Sets the internal state to "DATA" and stores remaining lines from |
| | the client in "received_data" until the terminator ""\r\n.\r\n"" is |
| | received. |
+----------+---------------------------------------------------------------------+
| HELP | Returns minimal information on command syntax |
+----------+---------------------------------------------------------------------+
| VRFY | Returns code 252 (the server doesn’t know if the address is valid) |
+----------+---------------------------------------------------------------------+
| EXPN | Reports that the command is not implemented. |
+----------+---------------------------------------------------------------------+
| 
