Question… How many black listed IP address can SmarterMail handle before it hits a list limit or compromises performance? 

I realize part of the answer is “hardware performance.” We’re running on a dedicated HP Proliant 8 core server with 32 GB of memory - plenty of performance. So the question is directed more at SmarterMail’s practical limitations.
 

Background… We use a spam filtering / security app that filters spam, monitors failed logins, detects various types of hacks and attacks and takes countermeasure by blacklisting the involved IP addresses in SmarterMail’s domain level blacklist via web services.
 

We recently encountered two coordinated brute force attacks. Collectively, the two attacks resulted in over 1,500 IP addresses being added to the SMTP blacklist. I’m concerned that 1,500+ might be close to or greater than the practical design limit for the blacklist. We're running the latest stable build of SmarterMail Version 14.