Spamassassin is slow - any tips or good commercial alternative?

[Rob Poe]

>>> 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"
> 
> Thank you James - this will be very helpful I suspect.
> We also are using Exim as the MTA, so any specific config advice for Exim 
> would also be greatly appreciated :)
> BTW we are using one server (Pentium 4, 2.4GHz, 1GB RAM), currently have 
> 1500 active paid users,
>  and am expecting up to 10,000-15,000 active paid users in the future (say, 
> 1 or 2 years from now).

I'd expect that only ONE P4 2.4 1g isn't enough ...  

If it were my configuration and I had that many users, I'd probably go more into the Core2/Xeon/some other kind of multi-core or multi processor setup, and go with at least 4 gigs of ram, making sure you also focus on using FAST drives (10k SAS raid0+1)