Spamassassin is slow - any tips or good commercial alternative?

James Gray james at
Thu Jun 19 00:53:05 IST 2008

On 18/06/2008, at 11:56 PM, Charlie wrote:

> The concern is that I am eventually looking to have over 10,000  
> users, so will be receiving, and then sending, multiple emails per  
> second.
> Even now, with only 1,500 users, people have started reporting "Too  
> many concurrent SMTP connections; Please try again later"

I manage a mail cluster for an ISP that has about 100,000 subscribers  
online at any given time.  I'd hazard a guess that close to all of  
those subscribers have a mail client running the whole time.  We have  
implemented an exim set up that allows 3 concurrent connections from  
the subscriber IP pools, 5 from from other IP's and a maximum number  
of simultaneous SMTP sessions of 1000 per server.  This is on each  
server in the cluster (4 servers in total) and we only ever see the  
maximum concurrent per IP rules being hit, never the maximum total.

As you didn't mention which MTA you're using, I can't give config  
examples, but make sure you pay close attention to the default max-per- 
IP and max-total SMTP session limits.  If these are still the  
defaults, they are probably far too restrictive for a multi-thousand  
user mail hub.  Also, if you're not already, put some thought into  
connection mitigation techniques such as RBL's, grey listing, etc.   
These will have a dramatic effect on external sites chewing up all  
your SMTP connections.  Also if your users are the sort of people who  
sit there smashing the "send and receive" button in their mail client,  
you may also want to think about rate-limiting connections from any  
single careful if you implement this, you can DoS your users  
if it isn't done right!!


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