Hello, Our company actually uses ISP Config 3 to admin a single mail physical server for about 600 domains and 1000 mailboxes : Server : Linux Debian Squeeze with ISP Config 3 Ram : 16GB CPU : 2 HD : 1TB We plan to reach a maximum of about 2000-3000 mailboxes in the years to come, so we would like to migrate to a more important mail architecture to prevent failures and to improve QoS (in particular ensure to keep short delays in receiving and sending mails). After having read several articles such as this one we look forward to install the following architecture (on virtual machines) : - 1 MX/smtp-in (local relay only) server, RAM 8GB, 2CPU, HD 0.1TB - 1 pop/imap/webmail server, RAM 8GB, 2CPU, HD 1TB - 1 smtp-out (authenticated relay only) server, RAM 4GB, 2CPU, HD 0.1TB Each server would run Linux Debian. RAM/CPU/HD are about the same as our current mail server for price reasons, we will be able to increase those thanks to the cloud Here are my questions : 1. Our setup is (on will) much more simple than the one presented on the article, because our company does not need to have a huge mail architecture, we just want a more robust and a "lightly" scalable architecture. Is this architecture correct ? Any suggestion is welcome 2. We plan to install ISP Config 3 only on the pop/imap/webmail server and to setup a MySql master/slave replication between this server and the two others, so that the smtp-in postfix server could use local lookup tables and the smtp-out postfix server could use local mysql table-based authentication. Is this right ? Or should we install ISP Config on each server ? 3. If (after a few years) we want to install one more pop/imap/webmail server, then how would the MX/smtp-in server know to which pop/imap server send mails ? Can this be done "directly" using ISP Config tables (for example using the field server_id ? Or should we use tools like Perdition ? Thank you EDIT : 4. In the years to come, we will surely add one more MX server and do DNS balancing. We noticed there are two solutions : Use a single IP address (ALIAS balancing) or use distinct IP adresses for each MX server (MX balancing). We thought the simpler solution would be doing ALIAS balancing because this would only imply adding an alias once for all domains, instead of having to define a new MX record for each domain. Is that correct ? Are there inconvenients to ALIAS balancing against MX balancing ?