[CentOS] Recommend Mail Server

Les Mikesell lesmikesell at gmail.com
Tue Nov 24 06:28:04 UTC 2009

Christopher Chan wrote:
>> If you have a reasonably fast internal mailer you can just let mimedefang on 
>> your external relay check against it with smtp in real time.  Exchange isn't one 
>> of those, though.
> That internal mailer still has to whack something. You would just be 
> adding another layer again with the smtp latency. What is with the love 
> of uber number of layers?

You are removing a layer if you just pass through the recipient check to the 
ultimate source (the internal delivery machine) before accepting, and it does in 
fact need to be able to handle the lookups at the speed real messages come in. 
However, your external relay is likely to get whacked with a dictionary attack 
that it needs to be able to reject quickly so you can't do that if the delivery 
box is slow.

I used qmail for one of my domains a while back and it's practice of accepting 
everything, then sending bounces got a dictionary attack onto some kind of 'good 
to spam' list and I got about 50,000 messages/day for non-existing users for 
years afterwards.  That was a problem until I put a sendmail with the good users 
in a virtuser table in front of it.  Interestingly, the messages would come in 
from a large number of different IP addresses but in a sorted order and with 
clearly coordinated timing.

   Les Mikesell
    lesmikesell at gmail.com

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