SMTP "Flood"

Posted on 2005-05-11
Last Modified: 2007-02-13
My incoming internet connection has been filling up with SMTP traffic like crazy basically stopping all other internet-based activitiy.   We have done all the Exchange 2003 stuff for stopping mail relay, and nothing has worked.  Any ideas?
Question by:jhunter9999
    LVL 15

    Accepted Solution

    Hi jhunter9999,
    Are these emails that you're receiving legitimate?

    In other words, are they correctly addressed to your users - or is it an attempt to relay?

    You can go to to check if your machine is acting as an opten relay.

    If the emails are legitimately addressed to your users, and you want to receive them, then you have two options:
    1 - Increase the bandwidth of your Internet connection
    2 - Configure a router/firewall with prioritisation to ensure that SMTP (port 25) traffic is handled as a low prority.

    Does that help?
    LVL 23

    Expert Comment

    If it is indeed relaying you have a couple options although I am not a secuity expert.

    1) Change the port number for SMTP (will slow down the attacks)

    2) Require authentication for SMTP


    Author Comment

    Turned out not to be relay, but some outbound queue corruption found by Microsoft suppot.  The router vendor did go in and setup some SMTP low-priority stuff, as a future precaution however   So, while not the exact solution, it was helpful to find out that the router had that capability, and it may prevent future problems

    Thanks to both of you however for responding.

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