[Gllug] Handling a new twist by spammers

[Xander D Harkness]

rich at annexia.org wrote:
> On Mon, Dec 09, 2002 at 02:43:57PM +0000, Xander D Harkness wrote:
> 
>>What I have done is to implement callout on the secondary mailservers, 
>>these then check with the primary that mail can be delivered and will 
>>only accept the mail once it has checked that it can forward it.
>>
>>This does cause a greater load and for heavily stressed mailservers it 
>>is inappropriate.
> 
> 
> Doesn't this kind of defeat the point of a second mailserver - ie.
> somewhere to deliver mail to when your primaries are down?
> 
> Rich.
> 
I agree with this on a smaller set up.

If you have a number of internal primaries with the internet facing 
mailservers sharing the load.  So that you have a couple or more relays 
on mx10 and a spare for emergencies on mx20 all deliveries are balanced 
on the relays.

The amount of spam that these knock off by consulting relay lists and 
using spam assassin etc can be great and the queries for usernames / 
deliveries is comparatively small against the internal servers.

The valid username checking is also relatively easy to set up in exim to 
do a query against an LDAP directory, NIS or MySQL database; thus taking 
this load away from the internal mail servers.  Many SMEs are running 
these sort of IP addressable databases.

Kind regards
Xander

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