On Fri, 26 May 2000, Muljawan Hendrianto wrote:

I am thinking about using QPOPPER+procmail, but some people say that it is not scalable because its authentication is based on /etc/passwd. And in Unix environment there is certain recommendation not to have more than 5000 users in /etc/passwd file.

That is outdated information, in my opinion. You should be able to control the scaling on that with sufficient machines in your cluster; for 20,000 users, /etc/passwd (or, one would hope, /etc/shadow) should be fine. Now, the question is; how sure are you you're not going to greatly exceed 20,000 users?