Load Balancing with Postfix [and SpamAssassin]

Michael L Torrie torriem at chem.byu.edu
Thu Jan 19 12:50:55 MST 2006

On Thu, 2006-01-19 at 11:29 -0700, Lonnie Olson wrote:
> Imagine a business client of yours needs to send you an email right 
> away.  Up until now your only contact has been via phone.  Now this 
> email will need to be responded to right away.  He sends it.  Your 
> server is now going to refuse it for a few hours.  After that, assuming 
> his mail server is configured to keep trying past those few hours, you 
> get the email, but look very bad to your client.

As we're constantly reminding our users, E-mail is, and never was
designed to be, an instant form of communication.  Nor is it intended to
be reliable, although it will try and try for days.  If you need to get
in touch with someone urgently, you should use a medium that is designed
for that, such as a voice call.  

Relying solely on e-mail is foolhardy, and does not make good business

E-mail will get through, or not at all.  It is simply a best-effort
system.  Nothing more, nothing less.  With today's level of e-mail
filtering, you can bet that with any given e-mail to any address at any
big company or ISP, there is a small chance your message will be
silently filtered out.  My point is that we (as administrators) should
not be misrepresenting to users what e-mail really is.

I think you misrepresent the delay and the effect that such a delay will
have.  The delay is usually much shorter than an hour.  And yes, I do
assume an e-mail server will retry.  Judging by my server's mail queue
logs, servers all over the world go down all the time temporarily for
any number of reasons.  E-mail server typically try to deliver mail for
up to three days.  To expect anything less would mean that e-mail just
simply couldn't work.

> Another problem is that of misconfigured servers.  I have run into some 
> that the retry schedule increases dramatically, this can cause mail to 
> be delayed a very long time.

This has proven to be a non-issue in practice.  All graylist solutions
I've seen have special logic to deal with such brain-dead servers.

> Basically, for your personal email it is a great way to reduce spam, but 
> keep that whitelist current.

I'll keep people posted on the results of our trials.


> --lonnie
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