Concepts
There are two general ways you can run the SMTP server, via the command line or programmatically.
There are several dimensions in which you can extend the basic functionality of the SMTP server. You can implement an event handler which uses well defined handler hooks that are called during the various steps in the SMTP dialog. If such a hook is implemented, it assumes responsibility for the status messages returned to the client.
You can also subclass the core SMTP
class to implement
new commands, or change the semantics of existing commands.
For example, if you wanted to print the received message on the console, you
could implement a handler that hooks into the DATA
command. The contents
of the message will be available on one of the hook’s arguments, and your
handler could print this content to stdout.
On the other hand, if you wanted to implement an SMTP-like server that adds a
new command called PING
, you would do this by subclassing SMTP
, adding
a method that implements whatever semantics for PING
that you want.
Sessions and envelopes
Two classes are used during the SMTP dialog with clients. Instances of these are passed to the handler hooks.
Note
Handler Hooks MAY add new attributes to these classes for inter-hook coordination.
Session
The session represents the state built up during a client’s socket connection to the server. Each time a client connects to the server, a new session object is created.
- class Session(loop)
- Parameters:
loop – asyncio event loop currently running
SMTP
.
- ssl
Defaulting to None, this attribute will contain some extra information, as a dictionary, from the
asyncio.sslproto.SSLProtocol
instance. This dictionary provides additional information about the connection. It contains implementation-specific information so its contents may change, but it should roughly correspond to the information available throughasyncio.BaseTransport.get_extra_info()
- host_name
Defaulting to None, this attribute will contain the host name argument as seen in the
HELO
orEHLO
(or for LMTP, theLHLO
) command.
- extended_smtp
Defaulting to False, this flag will be True when the
EHLO
greeting was seen, indicating ESMTP.
- loop
This is the asyncio event loop instance.
Handler Hooks can utilize this if needed, for instance invoking
call_later()
to set some timers.
- login_data
Contains the login information gathered during the
AUTH
procedure. If it containsNone
, that means authentication has not taken place or has failed.Warning
This is the “legacy” login_data, populated only if
auth_callback
parameter is set.Deprecated since version 1.3: This attribute will be removed in version 2.0.
- auth_data
Contains the authentication data returned by the
authenticator
callback.
Envelope
The envelope represents state built up during the client’s SMTP dialog. Each
time the protocol state is reset, a new envelope is created. E.g. when the
SMTP RSET
command is sent, the state is reset and a new envelope is
created. A new envelope is also created after the DATA
command is
completed, or in certain error conditions as mandated by RFC 5321.
- class Envelope
- mail_from: str
Defaulting to None, this attribute holds the email address given in the
MAIL FROM
command.
- mail_options: List[str]
Defaulting to None, this attribute contains a list of any ESMTP mail options provided by the client, such as those passed in by
smtplib.SMTP.sendmail()
- content: AnyStr
Defaulting to None, this attribute will contain the contents of the message as provided by the
DATA
command. If thedecode_data
parameter to theSMTP
constructor was True, then this attribute will contain the UTF-8 decoded string, otherwise it will contain the raw bytes.
- original_content: bytes
Defaulting to None, this attribute will contain the contents of the message as provided by the
DATA
command. Unlike thecontent
attribute, this attribute will always contain the raw bytes.
- rcpt_tos: List[str]
Defaulting to the empty list, this attribute will contain a list of the email addresses provided in the
RCPT TO
commands.
- rcpt_options: List[str]
Defaulting to the empty list, this attribute will contain the list of any recipient options provided by the client, such as those passed in by
smtplib.SMTP.sendmail()