Slightly OT: Choosing an outbound MTA Setup

[am.lists]

I have my inbound MTA as Postfix, coming into MailScanner. As my
hosting organization grows, I'm trying to scale as smartly as
possible.

The before picture (even before MailScanner) was a single box running
about 60 domains. Web, FTP, Mail (plus commercial spam/virus filtering
tools).

We suffered through enough DDOS and dictionary attacks on the mail
server that we could justify putting a MailScanner proxy into place.
While we're still converting domains over to that infrastructure,
We're now looking at sorting out the mail sendout piece.

I'd like to qo with either Qmail or Postfix on a dedicated box, this
way we can have the resources to just pump out the mail. We do a
considerable amount of newsletters / mail lists for our users (all
opt-in of course!),

My proposed config would be fairly light:
- MTA
- Domain Keys signing ability
- Administration (webmin, or something more than just ssh to manage it)

I'd also like to use domain keys on the outbound side to further
legitimize our messages.

Postfix has "dkfilter.out" for this, but I'm wondering if anyone here
has any suggestions.

PS: I purposely didn't go on to the Postfix list and ask "Postfix or
Qmail?" because I'm not sure I would have gotten the most unbiased
opinion there. :-P At least here I know people have epxerience with a
variety of configurations.

Thanks all,

Angelo