It is not possible to limit the number of processes or the amount of allowed memory?
I have no idea yet, sorry. You already limit process number in Postfix master.cf, you should reduce value of '$max_servers' in Amavisd config, not '$max_use'.
I also noticed that there is an Apache process running as "iredadmin" and one running as "root". Both are not the default and highly recommended default user "www-data". Is this initiated by Iredmail? Especially the root user is what is worrying me.
Both are required.
*) We configure iRedAdmin to run as a separate, non-priviliege system user, 'iredadmin' by default, better for security.
*) The root user, i believe it's used to start Apache daemon first, then chroot sub-processes to 'www-data'.
I implemented above suggestion by disabling outgoing contentscanning. It does not do a thing.
It's for outgoing emails, if you have lots of incoming emails, they will eat much system resource as usual.
As the server was fully rebooted an other (Jetty) process was started preventing mysql/mariadb to be started. Both require about 20% RAM. My goal is to allow them to run together, but I fail to see how this can be done without limiting the resources eaten by cbpolicyd, amavis and clam as they sum up to 60% of RAM regardless if it is a 512mb or 1 GB RAM VPS.
Sorry, what's 'Jetty' process? i don't know it at all.