large pop3 servers

[Chris Shenton]

Mike Tancsa <mike at sentex.net> writes:

> As our pop3 requirements grow I want to try and remove as many single
> points of failure as possible as well as scale the system as needed.
> Is there anything like
> http://www.remote.org/jochen/mail/popular/
> being used on FreeBSD ?  Does anyone have any pointers on building
> large scale load balanced pop3 systems ?

I prototyped on FreeBSD but my client's policies dictated a Solaris
deployment. :-( I used qmail + qmail-ldap, and use qmail's pop3d for
POP and POPS; I also offer courier-imap for IMAP and IMAPS.

I have 5 1U servers behind a pair of load balancers; one is the LDAP
master, the other are LDAP replicas which also run the MTA, POP and
IMAP servers.  They all store mail on a backend NFS server (NetApp).

(The POPular proxying thing seems like qmail-ldap's notion of
clustering which routes mail and users to their respective storage
servers.  I believe shared storage is more simple and doesn't cripple
a chunk of your users if one of the POPular storage servers goes down)

The thing that makes the shared storage possible is Maildir storage
rather than monolithic mbox-style files; it also greatly improves
performance.  On the system we're replacing (with qpopper), the disks
are constantly thrashing when users check for mail (scan entire file
looking for new stuff), while Maildir makes it a simple dir scan.
Even worse is when a user deletes a msg from an mbox, requiring
copying then copying back sans the target message.

Before deciding to go with an entire new system, I did a test using
the existing sendmail delivering via Maildrop into Maildirs, then used
qmail's pop3d to offer mail to users from the Maildirs.  It was much
much faster than the mbox. So you could go this route even if you're
not a inclined to use qmail.