Load Balancing with Postfix [and SpamAssassin]

Michael L Torrie torriem at chem.byu.edu
Fri Jan 20 13:14:29 MST 2006

On Fri, 2006-01-20 at 11:34 -0700, Ross Werner wrote:
> There's a huge difference between "no QoS" and "doesn't matter if you 
> intentionally add delays", however. There's no QoS for AIM, for instance, 
> but if AOL started started implementing a five-second delay for every 
> message (maybe "to fight instant messaging spam"), you can bet users would 
> be pissed.

A gray list mechanism doesn't introduce an intentional delay to every
single message.  After a short time, there are only a rare occasional
(much like the e-mail normally is).

IM and E-mail are fundamentally different and billed as such.  Thus to
compare IM to E-mail is kind of silly (as Stuart has already pointed


> The whole "best effort" excuse is pretty pitiful, in my opinion. IP does 
> not provide any sort of QoS and is "best effort delivery", but if your ISP 
> starts degrading IP performance, you're going to be upset.

It's not an excuse; it is fact.  

No IP is not "best effort."  TCP/IP is, though.  IP packets merely have
a source and a destination and they get sent on their way, the sender
never knowing if they will ever be delivered unless the transport on top
of IP has a machanism for that.  Anyway, like e-mail, TCP keeps trying
until it gets through or times out.  I'm always amazed how a tcp
connection can stay up over several minute physical outage.

Sure people would be upset (and will be if the big bells have their way)
if ip traffic is randomly degraded (which, ironically, is a main
mechanism for performing TCP/IP congestion control) , but you are
comparing apples and oranges here.  I understand your point, however.
And I counter it by saying that the very problems that gray listing is
striving to counter already cause these types of problems. For example,
spam and spam scanning already cause large organizations to have slow e-
mail delivery.  BYU itself sometimes can be as bad as a couple of hours.
Plus random dropping of e-mails (did your e-mail trigger the spam filter
or did it just get lost?  You'll never know).  At least if a gray list
ultimately causes a message to be rejected, you (the sender) will know
why and know for sure that it didn't make it, rather than wondering for

>  	~ Ross
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