Chuck Swiger <cswi...@mac.com> wrote:
> It's fairly common to scale up a mail infrastructure from one box
> handling both SMTP and IMAP (or POP) to a SMTP-only box writing to
> NFS-mounted user mailboxes, and have one or more dedicated reader
> boxes which only run IMAP/POP daemons which access that same NFS
> filesystem holding the user mailboxes.
Yikes! The _proper_ way to scale up from one box to multiple goes
something like this:
SMTP
Internet ---> mail.<domain> [original box]
This box now runs only the SMTP receiver, and perhaps
the spam/virus filtering (if it has enough capacity).
It contains no user mailboxes.
SMTP
mail.<domain> --+--> mailbox01.<domain>
| This box runs local delivery, and IMAP/POP
| daemons, for some user mailboxes (which are
| stored on _local_ disks). It may also handle
| spam/virus filtering for those mailboxes, if
| mail.<domain> can't handle that load.
|
+--> mailbox02.<domain>
| This box is just like mailbox01, for a different
| set of user mailboxes.
|
+--> mailbox03.<domain>
etc. -- as many as needed.
mail.<domain> becomes a multiplexer, so that the outside world can
send to <user>@mail.<domain> (or simply <user>@<domain> if you
prefer) without needing to know about the internal structure. The
multiplexing can be very simple, and thus very fast, by doing a
table-lookup based on the first character of <user>. There's no
need for NFS anywhere in the setup.
> ... I've been burned by NFS locking (mis)adventures in the past,
> and I hate to see people depend on it if they have alternatives....
As have I. Once. That was enough.
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