maillscanner/postfix saturates bandwidth :-(

Martin Hepworth maxsec at
Mon Sep 24 21:53:03 IST 2012

Seriously ... a 3.5mb mailout!
Drop the heavy content to a web server and point the html or downloadable
pdf or whatever from that.

Fixing the odd saturation is one thing but doing the job properly in the
first place would be better


On Monday, 24 September 2012, Harondel J. Sibble wrote:

> Had an odd situation that started Friday night at one of my clients
> running a
> mailscanner/mailwatch mail relay for their internal Exchange 2007 server.
> Basically the dsl connection they share with another office was saturated
> when the office admin did a mailout on friday to about 2000 of their
> subscribers, each email was about 3.5mb total with conversion overhead.
>  When
> I say saturated, I mean in both the upstream and downstream directions.
> According the admin who runs the multitenant network in this office, he was
> seeing a sustained 1.6mb/s INBOUND connection to my client's firewall while
> this was happening.
> I intially though that someone had hacked in and was injecting spam, but
> after upstream throttling of the connection and disabling all smtp
> traffic, I
> was able to review the messages in the postfix deferred queue and determine
> they were part of the mailout.
> At this point mailq was showing 14 messages with approx 100 recipients
> total,
> I could then re-enable smtp traffic (in/out) at the firewall level and
> emails
> would be fine sending and receiving, but if I did a postqueue -f, the
> connection would saturate again until I blocked the smtp traffic, then
> waited
> a couple minutes before re-enabling it and the messages went back to being
> deferred.
> I'm trying to figure out the best way to deal witih this moving forward, is
> there additional throttling I need to do at the postifx level or the
> mailscanner level or something else.  I was also surprised as my understand
> of postfix is that it does connection throttling by default.
> --
> Harondel J. Sibble
> Sibble Computer Consulting
> Creating Solutions for the small and medium business computer user.
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Martin Hepworth, CISSP
Oxford, UK
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