Quoting Cecil Eduardo Campos Costa (eduardo@ihatetelefonica.com):
> I would like to create a mail server with my NetBSD. Which one do you 
> recomend me for SMTP and for POP3? I was thinking in sendmail and fetch 
> but I would like to read some opinions.

I'd suggest and MTA that you are comfortable with and a POP
or IMAP server that can meet your undescribed needs.  I use
sendmail and spamassassin.

I use Sendmail Inc's IMAP server (commercial) on another OS
(I TRIED to get support for NetBSD/Sparc but they didn't
see the market I guess).  Cyrus is lovely and powerful.
Sieve is nice.

LDAP handles aliases and mail routing (and authentication,
and other stuff).

I know my setup could, with better disks, handle 100k users.
I have fewer than that (by nearly 100k :).  but it meets
my needs.