OT - Scalable email server solution needed

[Duane Whitty]

Hi,

My appologies in advance for the OT post.
This probably more appropriately belongs on ISP@ but
there doesn't seem to be much traffic there.

To the point:  I'm about to provide hosting services,
including but not limited to email, to a few local
business.  Right now I have Sendmail configured
and I was about to install Courier-IMAP.  My
concern is future scalability.  I'm not sure sendmail
is the right back-end MTA.  Right now Sendmail
and Procmail will work fine I believe with the addition
of an IMAP server.  But what about later on?

I was looking at DBmail but I'm not sure just how
much activity that project has so I'm a little leary,
but perhaps that's unjustified?  So now
I'm considering Exim or POSFIX.  The Sun Java
Communications Server looks appealing but unless
I misunderstood I don't have anywhere near the
bankroll for that yet and it doesn't look like a good
fit for a start-up operation anyhow.

I like that POPular port and the way it uses proxies etc.,
but it doesn't seem to support IMAP.

Is there anyone on the list who might be serving many
business customers each with many users who would
be willing to share their insights or opinions on this?

 From my past experiences, transitioning from a low volume
solution to a high volume solution, regardless of the application
domain, is usually best solved by making the right choice in
the beginning.  It would seem like an important marketing
tool as well.

If I am way of base here or missing something really
important I'd appreciate the heads-up.

Thanks in advance for any help.

Sincerely,

Duane