> Imagine there is a location with only one machine (Linux, PIII 650 with
> 256 MB Ram) handling some thousand users mailboxes with POP3. It is
> used for POP3 and SMTP.
A PII 450 with 512 MB RAM and a RAID can easily handle about 200.000
mailboxes, if all it does is POP3/IMAP and delivery to local mailboxes.
It depends a lot on the typical usage, but I assume you talk about the
mass market of dialup customers, if you want a scalable system.
You have to think about where to expand aliases and how to handle bounces
where the sender address is an alias and the like, but it can be done
without too many efforts.
> Additionally there are some "proxy" POP3-Servers in front of them
> that get the queries from the customer's mailclients. The POP3-Proxy
> looks the given User-ID up in a database and gets the information
> which internal POP3-Server and with what User-ID is in charge
> of that user's account. The POP3-Proxy connects to the internal
> machine, logs in with the internal ID and then we just forward
> the commands through the "proxy".
Been there, done that and found out that it works fine. Got the coffee
cup. :)
You may want to check the archives, where concepts for larger systems have
been described before. Check
http://www.moria.de/~michael/pop3proxyd/
for an ugly implementation of a pop3 proxy daemon and be aware that there
are others around.
Also consider other concepts besides a pop3 proxy. The global file system
GFS sounds very interesting, for example, but I have no experience with that
and it was not an option back then, when I designed my system.
Michael
