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I have a couple of messages appearing in my Postfix mail logs every day, like:

postfix/smtpd[7363]: warning: non-SMTP command from unknown[xx.xx.xx.xx]: GET / HTTP/1.0

Should I ignore them or block? If it is necessary block these attempts what is the best way to do this (iptables, postfix access maps, etc)?

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I use fail2ban. You can edit /etc/fail2ban/filter.d/postfix.conf to catch any further attempts. I monitor my /var/log/mail.log files to look for suspicious behaviour and add to postfix.conf as required. Here is my postfix.conf which does catch the line you mention above.

[INCLUDES]


before = common.conf

[Definition]

_daemon = postfix/smtpd

failregex = ^%(__prefix_line)sNOQUEUE: reject: RCPT from \S+\[<HOST>\]: 554 5\.7\.1 .*$
        ^%(__prefix_line)sNOQUEUE: reject: RCPT from \S+\[<HOST>\]: 450 4\.7\.1 : Helo       command rejected: Host not found; from=<> to=<> proto=ESMTP helo= *$
        ^%(__prefix_line)sNOQUEUE: reject: VRFY from \S+\[<HOST>\]: 550 5\.1\.1 .*$
        ^%(__prefix_line)sNOQUEUE: reject: RCPT from \S+\[<HOST>\]: 454 4\.7\.1 :*$
        reject: RCPT from (.*)\[<HOST>\]: 550 5.1.1
        reject: RCPT from (.*)\[<HOST>\]: 450 4.7.1
        reject: RCPT from (.*)\[<HOST>\]: 554 5.7.1
    reject: RCPT from unknown\[<HOST>\]: 454 4.7.1
    connect from unknown\[<HOST>\]

ignoreregex = 

you could also add

warning: non-SMTP command from unknown\[<HOST>\]:: GET / HTTP/1.0

if the above does not catch all.

If you wish to ban historical IP addresses manually then use IP tables.

Regards and good luck,

Matt

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There is no need to block "the command". If you find that someone is doing a ton of invalid commands block that IP address. A invalid command won't hurt anything, and is in some cases practical (i.e. supporting buggy clients).

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