void wrote:
>
> On Wed, Jun 20, 2001 at 12:04:22AM -0700, Matt Dillon wrote:
> >
> > A web proxy could be
> > round-robined fairly easily, but for a mail relay it
> > is often a good idea to split the incoming and outgoing
> > mail into two separate round robins (two separate groups
> > of machines).
>
> Why's that? So you can tune each type of machine appropriately for
> the task? How would you tune incoming and outgoing mail servers
> differently?
Outgoing mail servers and incoming mail servers have
different load characteristics and requirements.
Without giving away any intellectual property from my
own startup, here's a small sample:
o Incoming
SPAM filtering
+'ed address delivery
Virtual domains
Automated "spam" complaint handling
Automated "abuse" complaint handling
Virus scanning
Relay denial
Per domain mail queues
o Outgoing
Relay permitted for customers
SMTP-after-POP
SMTP AUTH
Exponential rate limiting, to avoid being a
SPAM source
Per message recipient count limiting ""
Total message count limiting
Outbound queue aging
Identd processing, to avoid 3 minute delays
DNS outage handling/avoidance
Queue aging
Queue division
Large queue processing
Hosted mailing list processing
Connection caching
That's about 1/3 my list for each of the two roles I've
chosen to disclose here.
In other words, it's a pretty big list, with a lot of
differences between the roles, translating into a lot of
differences between the tuning of both the applications
you run, and the servers themselves (you might even
decide to run sendmail in one direction, and qmail in
the other, based on operational characteristics).
FWIW: I designed and implemented (with help) the IBM
Web Connections NOC in Rochester New York, for pretty
much everything except the autoconfiguration database
for a specialized appliance. Matt was one of the
founders of Best Internet, Inc., which was bought out
by Verio.
Knowing how this stuff works is why Matt and I and
others were so offended at the "SysAdmin Magazine
``benchmark'' report on FreeBSD vs. other OSs": it
was not, as some have claimed, "sour grapes", it was
professional indignation.
-- Terry
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