Re: postscreen questions

From: Roderick A. Anderson (no email)
Date: Fri May 28 2010 - 13:52:50 EDT

  • Next message: Wietse Venema: "Re: postscreen questions"

    Andy Dills wrote:
    > On Thu, 27 May 2010, Wietse Venema wrote:
    >> Andy Dills:
    >>> I've been investigating postscreen, as we've been address probed/bombed
    >>> for years, as we have a few domains that are very old (well, early 90s)
    >>> that had a lot of users back in the dialup days. Our approach was to just
    >>> throw hardware at the problem, and we've had a whole cluster of servers
    >>> just sending out 550s all day long for years now.
    >>> We don't do any RBL checks at the postfix level; we have amavisd-new
    >>> handle all of that via spamassassin. I'm hesitant to allow a single
    >>> blacklist to determine the fate of mail acceptance, especially when we
    >>> have a very low false negative rate with amavisd/SA. Essentially, we'd
    >>> rather throw hardware at the problem than potentially reject legit mail.
    >>> My primary question is, would we see significant improvement by using
    >>> postscreen if we don't use RBLs?
    >> In my experience, the "pregreet" check kills off 50% of the zombies.
    >> Of course malware will "improve" and I expect to add deeper protocol
    >> checks (command pipelining, greylist) in anticipation.
    > That seems worth investigating, thank you. I appreciate how you're
    > evolving postfix to address this (and the improvements to handle content
    > filtering pre-queue, we will be moving to that once amavisd-new is more
    > mature with regards to that).
    >>> Also, would postscreen_cache_map work with a mysql backend?
    >> postscreen needs very low latency (I put in explicit tests for
    >> this). Also, postscreen requires read, write, iterate support
    >> which is implemented only for file-based databases.
    >> If table access requires 10ms, then postscreen can handle only 100
    >> connection requests per second. You would be better off not using
    >> postscreen and instead turning up the number of smtpd processes.
    > That makes sense. I was just looking for a way to provide some "shared
    > knowledge" among the servers in the cluster.

    Run a cron job that checks for changes in the RDBMS and then rebuilds
    the postscreen_cache_map "files" if needed.


    > Thanks,
    > Andy
    > ---
    > Andy Dills
    > Xecunet, Inc.
    > 301-682-9972
    > ---

  • Next message: Wietse Venema: "Re: postscreen questions"

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