How can I hold a SMTP connection open with smtplib and Python?

Question

I need to check the timeout of a SMTP-Server, but my socket just closes. What am I doing wrong? Here is my test for it:

#!/usr/bin/python
import smtplib
import time
import datetime
import socket
socket.setdefaulttimeout(1800)


now = time.time()
server = smtplib.SMTP()
server.set_debuglevel(1)
server.connect('mx.foo.bar','25')
(code,resp) = server.docmd('NOOP')
then = time.time()

print then-now

Lets hope this works.

Why do you want to do this? You connect, you send your mail, you disconnect. Why do you want to keep the connection open if you're not using it? — Jerry Coffin, Oct 20 '10 at 13:18
I'm trying to check RFC compliance. Python was suggested, instead of C for it's ease of use. — leto, Oct 20 '10 at 13:35

Ethan · Answer 1 · 2013-02-07T00:35:58.773

9

Well, I haven't found any method to hold a smtp connection open with smtplib.

But, if you want to reuse a connection without closing (yes, opening a connection takes time, 2-3 secs), you can test the connection first. To do this, issue a NOOP command and test for status == 250. If not, then you can open a connection and send out your mail. And you can choose to not quit() the connection until you are done.

import smtplib

def create_conn():
    conn = smtplib.SMTP('smtp.gmail.com', 587)
    ...
    return conn

def is_connected(conn):
    try:
        status = conn.noop()[0]
    except:  # smtplib.SMTPServerDisconnected
        status = -1
    return True if status == 250 else False

edited Feb 07 '13 at 00:35

answered Feb 03 '13 at 22:47

Ethan

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1

@Ethan- makes sense! – trex Feb 04 '16 at 11:34
1

@trex Thanks. And it works great, I have been using it successfully without any issue for the last 2+ yrs. – Ethan Feb 04 '16 at 15:06
This is a blocking method. Is it have timeout? – Minh Hoàng Aug 21 '19 at 01:25
1

This works fine, Create a global variable smtp_connection and check is_connected(smtp_connection) in your create_conn function and it will reuse the same connection until its closed or timeouts. – Ruchit Patel Feb 17 '21 at 08:46

score 1 · Answer 2 · answered Oct 20 '10 at 17:02

Are you sure you are disconnecting? When I run the above code against a postfix server I get:

connect: ('server', '25')
connect: ('ip.address', 25)
reply: '220 server ESMTP Postfix\r\n'
reply: retcode (220); Msg: nserver ESMTP Postfix
connect: server ESMTP Postfix
send: 'NOOP\r\n'
reply: '250 2.0.0 Ok\r\n'
reply: retcode (250); Msg: 2.0.0 Ok
0.0531799793243

The docmd does not block, the server responses and the program exits. I therefore disconnect when the program exits.

If I open a python command line and do:

>> import smtplib
>> server = smtplib.SMTP()
>> server.connect('server')
>> server.docmd('NOOP')
(250, '2.0.0 Ok')
>> ## let it sit for 5 minutes
>> server.docmd('NOOP')
(421, '4.4.2 server Error: timeout exceeded')

My logs confirm this:

Oct 20 10:45:35 [postfix/smtpd] connect from unknown[ip.address]
Oct 20 10:50:10 [postfix/smtpd] timeout after NOOP from unknown[ip.address]

score 0 · Answer 3 · answered Oct 20 '10 at 13:08

0

Check your mail server settings - they may be cutting the connection.

answered Oct 20 '10 at 13:08

Andrew Sledge

10,163
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It's happening with every MTA I checked. They get the command, return 220, then the connection is closed. Using telnet I get a timeout after 5 Minutes. – leto Oct 20 '10 at 13:12

How can I hold a SMTP connection open with smtplib and Python?

3 Answers3

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