Hi Till, thanks for your prompt reply but I still have a question:
.....This specific tutorial is based on my 256MB VPS.......
Spamassassin uses a lot of memory, so for a mail server with just a couple of users
1 child is plenty.
Do you know if there is any new services/functions that use in ISPConfig V3.x but not use in V2.x, such new services/functions might need more system memory? If this is not the case, do you mean that once the services/configuration is very similar between ISPConfig V2.x and V3.x, then the system memory requirement should be the same?