21.18. smtpd
— SMTP Server¶
Source code: Lib/smtpd.py
This module offers several classes to implement SMTP (email) servers.
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.
21.18.1. SMTPServer Objects¶
-
class
smtpd.
SMTPServer
(localaddr, remoteaddr, data_size_limit=33554432, map=None, enable_SMTPUTF8=False, decode_data=True)¶ Create a new
SMTPServer
object, which binds to local address localaddr. It will treat remoteaddr as an upstream SMTP relayer. It inherits fromasyncore.dispatcher
, and so will insert itself intoasyncore
‘s event loop on instantiation.data_size_limit specifies the maximum number of bytes that will be accepted in a
DATA
command. A value ofNone
or0
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 determins whether the
SMTPUTF8
extension (as defined in RFC 6531) should be enabled. The default isFalse
. If set toTrue
, decode_data must beFalse
(otherwise an error is raised). WhenTrue
,SMTPUTF8
is accepted as a parameter to theMAIL
command and when present is passed toprocess_message()
in thekwargs['mail_options']
list.decode_data specifies whether the data portion of the SMTP transaction should be decoded using UTF-8. The default is
True
for backward compatibility reasons, but will change toFalse
in Python 3.6; specify the keyword value explicitly to avoid theDeprecationWarning
. When decode_data is set toFalse
the server advertises the8BITMIME
extension (RFC 6152), accepts theBODY=8BITMIME
parameter to theMAIL
command, and when present passes it toprocess_message()
in thekwargs['mail_options']
list.-
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 toFalse
, it will be a bytes object.kwargs is a dictionary containing additional information. It is empty unless at least one of
decode_data=False
orenable_SMTPUTF8=True
was given as an init parameter, in which case 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 noRCPT 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 normal250 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 arguments, and the kwargs argument to
process_message()
when one or more of these is specified.-
21.18.2. 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.
21.18.3. 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.
21.18.4. 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.
21.18.5. SMTPChannel Objects¶
-
class
smtpd.
SMTPChannel
(server, conn, addr, data_size_limit=33554432, map=None, enable_SMTPUTF8=False, decode_data=True)¶ 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 ofNone
or0
means no limit.enable_SMTPUTF8 determins whether the
SMTPUTF8
extension (as defined in RFC 6531) should be enabled. The default isFalse
. AValueError
is raised if both enable_SMTPUTF8 and decode_data are set toTrue
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
True
for backward compatibility reasons, but will change toFalse
in Python 3.6. Specify the keyword value explicitly to avoid theDeprecationWarning
.To use a custom SMTPChannel implementation you need to override the
SMTPServer.channel_class
of yourSMTPServer
.Changed in version 3.5: the decode_data and enable_SMTPUTF8 arguments were added.
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 thenDATA
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()
.
The
SMTPChannel
operates by invoking methods namedsmtp_<command>
upon reception of a command line from the client. Built into the baseSMTPChannel
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
, andreceived_data
, but not the greeting.DATA Sets the internal state to DATA
and stores remaining lines from the client inreceived_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. -