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  1. #1

    SMPT and spam which case happened ?

    Hi all ..

    i have a dout and i want to make sure ..
    SMTP is used to transfer mail between servers !
    so when i want my system to function as a mail server i have to configure the SMTP .. okay ..if not cofnfigured well some hackers ( remote machine) send spam using my server ! Also the firewall must allow incoming mail .
    the above i think is right ! if somethign wrong tell me to update my info

    when i need to send email to a server .. say when i'm using mail client application such Mozilla mail or Evolution .. i need to configure the SMTP too , right ? but Firewall will not stop it . okay .. say the firewall is setted up .. no SMTP allowed using mail client .. configured the SMTP .. Do i have to pay attention to configuring as the above situation ( Mail server ) ? in other words "Can remote machines send spam using my system ? "
    i think the answer is "NO" ,, but still in dout

    thank you in advance

  2. #2
    Linux Guru
    Join Date
    Oct 2001
    Täby, Sweden
    I think I understand what you mean. If I do, you don't have to worry.

    First of all, the standard sendmail distribution that comes with most Linux distros is already configured by default both to not allow remote relaying, and to only listen to the localhost address, so sending SPAM via your machine is not possible for that reason alone.

    Second, when you use SMTP with your mail user agent (MUA), it's slightly different from the firewall's point of view. The SMTP that you blockusing the firewall is only incoming SMTP connections - ie. packets that are sent to port 25 (port 25 is the SMTP default port) on your system. When your MUA connects to the SMTP port of whatever mail server you're using, it uses a port number above 1024 on your system to connect to port 25 on the remote server. Ports above 1024 are normally not blocked by the firewall.

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