Postfix postfix/smtpd[3261]: lost connection after UNKNOWN from unknown[

Discussion in 'Server Operation' started by alanef, Apr 7, 2014.

  1. alanef

    alanef New Member


    I'm new to this forum, but I have come here as I have a specific problem and after searching the web I found very little about this, and this forum seemed to be the best place to start asking.

    My production mail server supports about 100 people and about 600/1000 emails a day.

    But it gets around 20,000 lost connections from UNKNOWN per day, with a typical UNKNOWN IP address creating 300/400 each.

    Here is a log summary
    Connections lost:
    Connection lost while AUTH : 20 Time(s)
    Connection lost while CONNECT : 1267 Time(s)
    Connection lost while EHLO : 1 Time(s)
    Connection lost while END-OF-MESSAGE : 1 Time(s)
    Connection lost while NOOP : 1 Time(s)
    Connection lost while RCPT : 49 Time(s)
    Connection lost while RSET : 1 Time(s)
    Connection lost while UNKNOWN : 17645 Time(s)

    On my test / secondary server (which handles about 80 emails a day) I dont get any Connection lost while UNKNOWN

    What is going on, is the a DOS (it been going on for at least a month) or spambots or brute force attempts, or similar?

    I have had some complaints about server connections not being made, and I can't see anything specific in the logs apart from all these entries, so will this number of lost connections materially impact the performance?

    If so should I do something like fail2ban the UNKOWN/unkowns, or could it be something else like a bad config setting?

    I think my server is more than powerful enough to handle the normal load.

    Any thoughts or areas to look at, gratefully received.
  2. Acceos

    Acceos New Member


    That sounds weird.

    Are you running Linux/BSD?

    What Distro?

    Please supply more lines from the log

    Include postfix conf
  3. hereinoz

    hereinoz Member

    Sounds a bit like someone is running a botnet to have a go at a brute force attack. They usually go away after a while then come back and have another go later.

    20,000 (about 1 every 4 seconds) is a lot, and probably will be impacting on the server's ability to receive legitimate mail. Not sure what you can do about it though. Perhaps someone with far more knowledge of these things will come up with an answer.

    To my knowledge you can't stop people trying to connect with your server, unless you block the specific IP addresses, and how can you block the IP address if it is UNKNOWN?

    Have you tested the server to see how it presents to the outside world?
  4. Olgierd

    Olgierd Member

    lost connection after UNKNOWN from unknown


    I have the same problem. Did you figure out this?
    How to solve this issue ?
  5. srijan

    srijan New Member HowtoForge Supporter


    Which tutorial you have used for the server? Are there any other errors in your mail log?
    What's the output of
  6. Olgierd

    Olgierd Member

    Server was setup about 3 yr ago and worked fine. I used Perfect server ISPconfig3 on debian.

    I have only this errors.
    [QUOTE]Jul 17 07:05:46 ns2 postfix/smtpd[15243]: lost connection after CONNECT from[]
    Jul 17 07:05:46 ns2 postfix/smtpd[15243]: disconnect from[]
    Jul 17 07:05:46 ns2 postfix/smtpd[17210]: connect from unknown[]
    Jul 17 07:05:46 ns2 postfix/smtpd[9843]: warning: address not listed for hostname
    Jul 17 07:05:46 ns2 postfix/smtpd[9843]: connect from unknown[]
    Jul 17 07:05:47 ns2 postfix/smtpd[16539]: connect from[]
    Jul 17 07:05:47 ns2 postfix/smtpd[16539]: 1DEBC11E923A:[]
    Jul 17 07:05:47 ns2 postfix/smtpd[13345]: connect from unknown[]
    root@ns2:~# netstat -tap
    Active Internet connections (servers and established)
    Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
    tcp        0      0 localhost.localdo:10024 *:*                     LISTEN      16820/amavisd (ch9-
    tcp        0      0 localhost.localdo:10025 *:*                     LISTEN      10620/smtpd
    tcp        0      0 *:mysql                 *:*                     LISTEN      17366/mysqld
    tcp        0      0 *:submission            *:*                     LISTEN      13733/master
    tcp        0      0 localhost.localdo:11211 *:*                     LISTEN      3026/memcached
    tcp        0      0 *:pop3                  *:*                     LISTEN      3367/dovecot
    tcp        0      0 *:imap2                 *:*                     LISTEN      3367/dovecot
    tcp        0      0 localhost.localdo:spamd *:*                     LISTEN      3142/
    Last edited: Jul 17, 2014
  7. srijan

    srijan New Member HowtoForge Supporter

    The possible reason could be
    1) The dns record is not corrcet.
    2) Port 25 is not forwarded from router to the server IP if your server is installed in a local network.
    3) Port 25 is blocked by a firewall on the server, a router or by your ISP.
    4) Postfix is not listening on the external network interface.

    Please post the output of:


  8. Olgierd

    Olgierd Member

    -N INT_IN
    -N INT_OUT
    -N PUB_IN
    -N PUB_OUT
    -N fail2ban-apache-nohome
    -N fail2ban-apache-overflows
    -N fail2ban-dovecot-pop3imap
    -N fail2ban-postfix
    -N fail2ban-pureftpd
    -N fail2ban-ssh
    A INPUT -p tcp -m multiport --dports 25,465 -j fail2ban-postfix
    -A INPUT -p tcp -m multiport --dports 22 -j fail2ban-ssh
    -A INPUT -p tcp -m multiport --dports 21 -j fail2ban-pureftpd
    -A INPUT -p tcp -m multiport --dports 80,443 -j fail2ban-apache-overflows
    -A INPUT -p tcp -m multiport --dports 80,443 -j fail2ban-apache-nohome
    -A INPUT -p tcp -m multiport --dports 110,995,143,993 -j fail2ban-dovecot-pop3imap
    -A INPUT -d ! -i lo -p tcp -j DROP
    -A INPUT -i lo -j ACCEPT
    -A INPUT -s -j DROP
    -A INPUT -i eth+ -j PUB_IN
    -A INPUT -i ppp+ -j PUB_IN
    -A INPUT -i slip+ -j PUB_IN
    -A INPUT -i venet+ -j PUB_IN
    -A INPUT -i bond+ -j PUB_IN
    -A INPUT -j DROP
    -A OUTPUT -o eth+ -j PUB_OUT
    -A OUTPUT -o ppp+ -j PUB_OUT
    -A OUTPUT -o slip+ -j PUB_OUT
    -A OUTPUT -o venet+ -j PUB_OUT
    -A OUTPUT -o bond+ -j PUB_OUT
    -A INT_IN -p icmp -j ACCEPT
    -A INT_IN -j DROP
    -A INT_OUT -p icmp -j ACCEPT
    -A PUB_IN -p icmp -m icmp --icmp-type 3 -j ACCEPT
    -A PUB_IN -p icmp -m icmp --icmp-type 0 -j ACCEPT
    -A PUB_IN -p icmp -m icmp --icmp-type 11 -j ACCEPT
    -A PUB_IN -p icmp -m icmp --icmp-type 8 -j ACCEPT
    -A PUB_IN -p tcp -m tcp --dport 20 -j PAROLE
    -A PUB_IN -p tcp -m tcp --dport 21 -j PAROLE
    -A PUB_IN -p tcp -m tcp --dport 22 -j PAROLE
    -A PUB_IN -p tcp -m tcp --dport 25 -j PAROLE
    -A PUB_IN -p tcp -m tcp --dport 53 -j PAROLE
    -A PUB_IN -p tcp -m tcp --dport 80 -j PAROLE
    -A PUB_IN -p tcp -m tcp --dport 110 -j PAROLE
    -A PUB_IN -p tcp -m tcp --dport 143 -j PAROLE
    -A PUB_IN -p tcp -m tcp --dport 443 -j PAROLE
    -A PUB_IN -p tcp -m tcp --dport 465 -j PAROLE
    -A PUB_IN -p tcp -m tcp --dport 587 -j PAROLE
    -A PUB_IN -p tcp -m tcp --dport 993 -j PAROLE
    -A PUB_IN -p tcp -m tcp --dport 995 -j PAROLE
    -A PUB_IN -p tcp -m tcp --dport 3306 -j PAROLE
    -A PUB_IN -p tcp -m tcp --dport 8080 -j PAROLE
    -A PUB_IN -p tcp -m tcp --dport 8082 -j PAROLE
    -A PUB_IN -p tcp -m tcp --dport 10000 -j PAROLE
    -A PUB_IN -p tcp -m tcp --dport 50000:51000 -j PAROLE
    -A PUB_IN -p udp -m udp --dport 53 -j ACCEPT
    -A PUB_IN -p udp -m udp --dport 3306 -j ACCEPT
    -A PUB_IN -p icmp -j DROP
    -A PUB_IN -j DROP
    -A fail2ban-apache-nohome -j RETURN
    -A fail2ban-apache-overflows -j RETURN
    -A fail2ban-dovecot-pop3imap -s -j DROP
    -A fail2ban-dovecot-pop3imap -j RETURN
    -A fail2ban-postfix -j RETURN
    -A fail2ban-pureftpd -s -j DROP
    -A fail2ban-pureftpd -j RETURN
    -A fail2ban-ssh -s -j DROP
    -A fail2ban-ssh -s -j DROP
    -A fail2ban-ssh -s -j DROP
    -A fail2ban-ssh -j RETURN
  9. Acceos

    Acceos New Member


    What's the hostname and IP?

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