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.