Python 3.6.5 Documentation >  "smtplib" — SMTP protocol client

"smtplib" — SMTP protocol client
********************************

**Source code:** Lib/smtplib.py

======================================================================

The "smtplib" module defines an SMTP client session object that can be
used to send mail to any Internet machine with an SMTP or ESMTP
listener daemon. For details of SMTP and ESMTP operation, consult
**RFC 821** (Simple Mail Transfer Protocol) and **RFC 1869** (SMTP
Service Extensions).

class smtplib.SMTP(host='', port=0, local_hostname=None[, timeout], source_address=None)

An "SMTP" instance encapsulates an SMTP connection. It has methods
that support a full repertoire of SMTP and ESMTP operations. If the
optional host and port parameters are given, the SMTP "connect()"
method is called with those parameters during initialization. If
specified, *local_hostname* is used as the FQDN of the local host
in the HELO/EHLO command. Otherwise, the local hostname is found
using "socket.getfqdn()". If the "connect()" call returns anything
other than a success code, an "SMTPConnectError" is raised. The
optional *timeout* parameter specifies a timeout in seconds for
blocking operations like the connection attempt (if not specified,
the global default timeout setting will be used). If the timeout
expires, "socket.timeout" is raised. The optional source_address
parameter allows binding to some specific source address in a
machine with multiple network interfaces, and/or to some specific
source TCP port. It takes a 2-tuple (host, port), for the socket to
bind to as its source address before connecting. If omitted (or if
host or port are "''" and/or 0 respectively) the OS default
behavior will be used.

For normal use, you should only require the initialization/connect,
"sendmail()", and "quit()" methods. An example is included below.

The "SMTP" class supports the "with" statement. When used like
this, the SMTP "QUIT" command is issued automatically when the
"with" statement exits. E.g.:

>>> from smtplib import SMTP
>>> with SMTP("domain.org") as smtp:
... smtp.noop()
...
(250, b'Ok')
>>>

Changed in version 3.3: Support for the "with" statement was added.

Changed in version 3.3: source_address argument was added.

New in version 3.5: The SMTPUTF8 extension (**RFC 6531**) is now
supported.

class smtplib.SMTP_SSL(host='', port=0, local_hostname=None, keyfile=None, certfile=None[, timeout], context=None, source_address=None)

An "SMTP_SSL" instance behaves exactly the same as instances of
"SMTP". "SMTP_SSL" should be used for situations where SSL is
required from the beginning of the connection and using
"starttls()" is not appropriate. If *host* is not specified, the
local host is used. If *port* is zero, the standard SMTP-over-SSL
port (465) is used. The optional arguments *local_hostname*,
*timeout* and *source_address* have the same meaning as they do in
the "SMTP" class. *context*, also optional, can contain a
"SSLContext" and allows configuring various aspects of the secure
connection. Please read Security considerations for best
practices.

*keyfile* and *certfile* are a legacy alternative to *context*, and
can point to a PEM formatted private key and certificate chain file
for the SSL connection.

Changed in version 3.3: *context* was added.

Changed in version 3.3: source_address argument was added.

Changed in version 3.4: The class now supports hostname check with
"ssl.SSLContext.check_hostname" and *Server Name Indication* (see
"ssl.HAS_SNI").

Deprecated since version 3.6: *keyfile* and *certfile* are
deprecated in favor of *context*. Please use
"ssl.SSLContext.load_cert_chain()" instead, or let
"ssl.create_default_context()" select the system’s trusted CA
certificates for you.

class smtplib.LMTP(host='', port=LMTP_PORT, local_hostname=None, source_address=None)

The LMTP protocol, which is very similar to ESMTP, is heavily based
on the standard SMTP client. It’s common to use Unix sockets for
LMTP, so our "connect()" method must support that as well as a
regular host:port server. The optional arguments local_hostname and
source_address have the same meaning as they do in the "SMTP"
class. To specify a Unix socket, you must use an absolute path for
*host*, starting with a ‘/’.

Authentication is supported, using the regular SMTP mechanism. When
using a Unix socket, LMTP generally don’t support or require any
authentication, but your mileage might vary.

A nice selection of exceptions is defined as well:

exception smtplib.SMTPException

Subclass of "OSError" that is the base exception class for all the
other exceptions provided by this module.

Changed in version 3.4: SMTPException became subclass of "OSError"

exception smtplib.SMTPServerDisconnected

This exception is raised when the server unexpectedly disconnects,
or when an attempt is made to use the "SMTP" instance before
connecting it to a server.

exception smtplib.SMTPResponseException

Base class for all exceptions that include an SMTP error code.
These exceptions are generated in some instances when the SMTP
server returns an error code. The error code is stored in the
"smtp_code" attribute of the error, and the "smtp_error" attribute
is set to the error message.

exception smtplib.SMTPSenderRefused

Sender address refused. In addition to the attributes set by on
all "SMTPResponseException" exceptions, this sets ‘sender’ to the
string that the SMTP server refused.

exception smtplib.SMTPRecipientsRefused

All recipient addresses refused. The errors for each recipient are
accessible through the attribute "recipients", which is a
dictionary of exactly the same sort as "SMTP.sendmail()" returns.

exception smtplib.SMTPDataError

The SMTP server refused to accept the message data.

exception smtplib.SMTPConnectError

Error occurred during establishment of a connection with the
server.

exception smtplib.SMTPHeloError

The server refused our "HELO" message.

exception smtplib.SMTPNotSupportedError

The command or option attempted is not supported by the server.

New in version 3.5.

exception smtplib.SMTPAuthenticationError

SMTP authentication went wrong. Most probably the server didn’t
accept the username/password combination provided.

See also:

**RFC 821** - Simple Mail Transfer Protocol
Protocol definition for SMTP. This document covers the model,
operating procedure, and protocol details for SMTP.

**RFC 1869** - SMTP Service Extensions
Definition of the ESMTP extensions for SMTP. This describes a
framework for extending SMTP with new commands, supporting
dynamic discovery of the commands provided by the server, and
defines a few additional commands.

SMTP Objects
============

An "SMTP" instance has the following methods:

SMTP.set_debuglevel(level)

Set the debug output level. A value of 1 or "True" for *level*
results in debug messages for connection and for all messages sent
to and received from the server. A value of 2 for *level* results
in these messages being timestamped.

Changed in version 3.5: Added debuglevel 2.

SMTP.docmd(cmd, args='')

Send a command *cmd* to the server. The optional argument *args*
is simply concatenated to the command, separated by a space.

This returns a 2-tuple composed of a numeric response code and the
actual response line (multiline responses are joined into one long
line.)

In normal operation it should not be necessary to call this method
explicitly. It is used to implement other methods and may be useful
for testing private extensions.

If the connection to the server is lost while waiting for the
reply, "SMTPServerDisconnected" will be raised.

SMTP.connect(host='localhost', port=0)

Connect to a host on a given port. The defaults are to connect to
the local host at the standard SMTP port (25). If the hostname ends
with a colon ("':'") followed by a number, that suffix will be
stripped off and the number interpreted as the port number to use.
This method is automatically invoked by the constructor if a host
is specified during instantiation. Returns a 2-tuple of the
response code and message sent by the server in its connection
response.

SMTP.helo(name='')

Identify yourself to the SMTP server using "HELO". The hostname
argument defaults to the fully qualified domain name of the local
host. The message returned by the server is stored as the
"helo_resp" attribute of the object.

In normal operation it should not be necessary to call this method
explicitly. It will be implicitly called by the "sendmail()" when
necessary.

SMTP.ehlo(name='')

Identify yourself to an ESMTP server using "EHLO". The hostname
argument defaults to the fully qualified domain name of the local
host. Examine the response for ESMTP option and store them for use
by "has_extn()". Also sets several informational attributes: the
message returned by the server is stored as the "ehlo_resp"
attribute, "does_esmtp" is set to true or false depending on
whether the server supports ESMTP, and "esmtp_features" will be a
dictionary containing the names of the SMTP service extensions this
server supports, and their parameters (if any).

Unless you wish to use "has_extn()" before sending mail, it should
not be necessary to call this method explicitly. It will be
implicitly called by "sendmail()" when necessary.

SMTP.ehlo_or_helo_if_needed()

This method call "ehlo()" and or "helo()" if there has been no
previous "EHLO" or "HELO" command this session. It tries ESMTP
"EHLO" first.

"SMTPHeloError"
The server didn’t reply properly to the "HELO" greeting.

SMTP.has_extn(name)

Return "True" if *name* is in the set of SMTP service extensions
returned by the server, "False" otherwise. Case is ignored.

SMTP.verify(address)

Check the validity of an address on this server using SMTP "VRFY".
Returns a tuple consisting of code 250 and a full **RFC 822**
address (including human name) if the user address is valid.
Otherwise returns an SMTP error code of 400 or greater and an error
string.

Note: Many sites disable SMTP "VRFY" in order to foil spammers.

SMTP.login(user, password, *, initial_response_ok=True)

Log in on an SMTP server that requires authentication. The
arguments are the username and the password to authenticate with.
If there has been no previous "EHLO" or "HELO" command this
session, this method tries ESMTP "EHLO" first. This method will
return normally if the authentication was successful, or may raise
the following exceptions:

"SMTPHeloError"
The server didn’t reply properly to the "HELO" greeting.

"SMTPAuthenticationError"
The server didn’t accept the username/password combination.

"SMTPNotSupportedError"
The "AUTH" command is not supported by the server.

"SMTPException"
No suitable authentication method was found.

Each of the authentication methods supported by "smtplib" are tried
in turn if they are advertised as supported by the server. See
"auth()" for a list of supported authentication methods.
*initial_response_ok* is passed through to "auth()".

Optional keyword argument *initial_response_ok* specifies whether,
for authentication methods that support it, an “initial response”
as specified in **RFC 4954** can be sent along with the "AUTH"
command, rather than requiring a challenge/response.

Changed in version 3.5: "SMTPNotSupportedError" may be raised, and
the *initial_response_ok* parameter was added.

SMTP.auth(mechanism, authobject, *, initial_response_ok=True)

Issue an "SMTP" "AUTH" command for the specified authentication
*mechanism*, and handle the challenge response via *authobject*.

*mechanism* specifies which authentication mechanism is to be used
as argument to the "AUTH" command; the valid values are those
listed in the "auth" element of "esmtp_features".

*authobject* must be a callable object taking an optional single
argument:

data = authobject(challenge=None)

If optional keyword argument *initial_response_ok* is true,
"authobject()" will be called first with no argument. It can
return the **RFC 4954** “initial response” bytes which will be
encoded and sent with the "AUTH" command as below. If the
"authobject()" does not support an initial response (e.g. because
it requires a challenge), it should return "None" when called with
"challenge=None". If *initial_response_ok* is false, then
"authobject()" will not be called first with "None".

If the initial response check returns "None", or if
*initial_response_ok* is false, "authobject()" will be called to
process the server’s challenge response; the *challenge* argument
it is passed will be a "bytes". It should return "bytes" *data*
that will be base64 encoded and sent to the server.

The "SMTP" class provides "authobjects" for the "CRAM-MD5",
"PLAIN", and "LOGIN" mechanisms; they are named
"SMTP.auth_cram_md5", "SMTP.auth_plain", and "SMTP.auth_login"
respectively. They all require that the "user" and "password"
properties of the "SMTP" instance are set to appropriate values.

User code does not normally need to call "auth" directly, but can
instead call the "login()" method, which will try each of the above
mechanisms in turn, in the order listed. "auth" is exposed to
facilitate the implementation of authentication methods not (or not
yet) supported directly by "smtplib".

New in version 3.5.

SMTP.starttls(keyfile=None, certfile=None, context=None)

Put the SMTP connection in TLS (Transport Layer Security) mode.
All SMTP commands that follow will be encrypted. You should then
call "ehlo()" again.

If *keyfile* and *certfile* are provided, these are passed to the
"socket" module’s "ssl()" function.

Optional *context* parameter is a "ssl.SSLContext" object; This is
an alternative to using a keyfile and a certfile and if specified
both *keyfile* and *certfile* should be "None".

If there has been no previous "EHLO" or "HELO" command this
session, this method tries ESMTP "EHLO" first.

"SMTPHeloError"
The server didn’t reply properly to the "HELO" greeting.

"SMTPNotSupportedError"
The server does not support the STARTTLS extension.

"RuntimeError"
SSL/TLS support is not available to your Python interpreter.

Changed in version 3.3: *context* was added.

Changed in version 3.4: The method now supports hostname check with
"SSLContext.check_hostname" and *Server Name Indicator* (see
"HAS_SNI").

Changed in version 3.5: The error raised for lack of STARTTLS
support is now the "SMTPNotSupportedError" subclass instead of the
base "SMTPException".

SMTP.sendmail(from_addr, to_addrs, msg, mail_options=[], rcpt_options=[])

Send mail. The required arguments are an **RFC 822** from-address
string, a list of **RFC 822** to-address strings (a bare string
will be treated as a list with 1 address), and a message string.
The caller may pass a list of ESMTP options (such as "8bitmime") to
be used in "MAIL FROM" commands as *mail_options*. ESMTP options
(such as "DSN" commands) that should be used with all "RCPT"
commands can be passed as *rcpt_options*. (If you need to use
different ESMTP options to different recipients you have to use the
low-level methods such as "mail()", "rcpt()" and "data()" to send
the message.)

Note: The *from_addr* and *to_addrs* parameters are used to
construct the message envelope used by the transport agents.
"sendmail" does not modify the message headers in any way.

*msg* may be a string containing characters in the ASCII range, or
a byte string. A string is encoded to bytes using the ascii codec,
and lone "\r" and "\n" characters are converted to "\r\n"
characters. A byte string is not modified.

If there has been no previous "EHLO" or "HELO" command this
session, this method tries ESMTP "EHLO" first. If the server does
ESMTP, message size and each of the specified options will be
passed to it (if the option is in the feature set the server
advertises). If "EHLO" fails, "HELO" will be tried and ESMTP
options suppressed.

This method will return normally if the mail is accepted for at
least one recipient. Otherwise it will raise an exception. That
is, if this method does not raise an exception, then someone should
get your mail. If this method does not raise an exception, it
returns a dictionary, with one entry for each recipient that was
refused. Each entry contains a tuple of the SMTP error code and
the accompanying error message sent by the server.

If "SMTPUTF8" is included in *mail_options*, and the server
supports it, *from_addr* and *to_addrs* may contain non-ASCII
characters.

This method may raise the following exceptions:

"SMTPRecipientsRefused"
All recipients were refused. Nobody got the mail. The
"recipients" attribute of the exception object is a dictionary
with information about the refused recipients (like the one
returned when at least one recipient was accepted).

"SMTPHeloError"
The server didn’t reply properly to the "HELO" greeting.

"SMTPSenderRefused"
The server didn’t accept the *from_addr*.

"SMTPDataError"
The server replied with an unexpected error code (other than a
refusal of a recipient).

"SMTPNotSupportedError"
"SMTPUTF8" was given in the *mail_options* but is not supported
by the server.

Unless otherwise noted, the connection will be open even after an
exception is raised.

Changed in version 3.2: *msg* may be a byte string.

Changed in version 3.5: "SMTPUTF8" support added, and
"SMTPNotSupportedError" may be raised if "SMTPUTF8" is specified
but the server does not support it.

SMTP.send_message(msg, from_addr=None, to_addrs=None, mail_options=[], rcpt_options=[])

This is a convenience method for calling "sendmail()" with the
message represented by an "email.message.Message" object. The
arguments have the same meaning as for "sendmail()", except that
*msg* is a "Message" object.

If *from_addr* is "None" or *to_addrs* is "None", "send_message"
fills those arguments with addresses extracted from the headers of
*msg* as specified in **RFC 5322**: *from_addr* is set to the
*Sender* field if it is present, and otherwise to the *From* field.
*to_addrs* combines the values (if any) of the *To*, *Cc*, and
*Bcc* fields from *msg*. If exactly one set of *Resent-** headers
appear in the message, the regular headers are ignored and the
*Resent-** headers are used instead. If the message contains more
than one set of *Resent-** headers, a "ValueError" is raised, since
there is no way to unambiguously detect the most recent set of
*Resent-* headers.

"send_message" serializes *msg* using "BytesGenerator" with "\r\n"
as the *linesep*, and calls "sendmail()" to transmit the resulting
message. Regardless of the values of *from_addr* and *to_addrs*,
"send_message" does not transmit any *Bcc* or *Resent-Bcc* headers
that may appear in *msg*. If any of the addresses in *from_addr*
and *to_addrs* contain non-ASCII characters and the server does not
advertise "SMTPUTF8" support, an "SMTPNotSupported" error is
raised. Otherwise the "Message" is serialized with a clone of its
"policy" with the "utf8" attribute set to "True", and "SMTPUTF8"
and "BODY=8BITMIME" are added to *mail_options*.

New in version 3.2.

New in version 3.5: Support for internationalized addresses
("SMTPUTF8").

SMTP.quit()

Terminate the SMTP session and close the connection. Return the
result of the SMTP "QUIT" command.

Low-level methods corresponding to the standard SMTP/ESMTP commands
"HELP", "RSET", "NOOP", "MAIL", "RCPT", and "DATA" are also supported.
Normally these do not need to be called directly, so they are not
documented here. For details, consult the module code.

SMTP Example
============

This example prompts the user for addresses needed in the message
envelope (‘To’ and ‘From’ addresses), and the message to be delivered.
Note that the headers to be included with the message must be included
in the message as entered; this example doesn’t do any processing of
the **RFC 822** headers. In particular, the ‘To’ and ‘From’ addresses
must be included in the message headers explicitly.

import smtplib

def prompt(prompt):
return input(prompt).strip()

fromaddr = prompt("From: ")
toaddrs = prompt("To: ").split()
print("Enter message, end with ^D (Unix) or ^Z (Windows):")

# Add the From: and To: headers at the start!
msg = ("From: %s\r\nTo: %s\r\n\r\n"
% (fromaddr, ", ".join(toaddrs)))
while True:
try:
line = input()
except EOFError:
break
if not line:
break
msg = msg + line

print("Message length is", len(msg))

server = smtplib.SMTP('localhost')
server.set_debuglevel(1)
server.sendmail(fromaddr, toaddrs, msg)
server.quit()

Note: In general, you will want to use the "email" package’s
features to construct an email message, which you can then send via
"send_message()"; see email: Examples.