OT: building new server, need MTA advice

[Chris Yuzik]

We're in the process of building what will be our new web and mail 
server. We will be hosting several virtual domains and each will have 
anywhere from a few to a couple of hundred email users. Obviously we 
will be running MailScanner and also MailWatch. The box is running 
CentOS 4.4 (it's like RHEL).

Since we're starting fresh on this box, we're not necessarily married to 
Sendmail like on our other servers. We could stick with Sendmail, or we 
could move over to Postfix or Exim (anything else worth considering?). 
We'd like to be able to add new spam-fighting features as they come out, 
such as the greet-pause and such. Over the years we've used Sendmail, 
I've found it a bear to tweak so have done the absolute minimum with it. 
We're looking for something that is secure, efficient, maintained (which 
rules out qmail) and easy to administer. Whatever we look at needs to 
play very nicely with MailScanner or it's not worth considering. 
Finally, (and I'm not sure it makes a difference to the MTA), we need 
our users to be able to log in with the "username at domain.tld" format 
because that's what they use now and I don't want to have to change 
hundreds of user's email client settings.

Now for the big question: Is there an MTA that should we consider using 
instead of Sendmail?

Thanks,
Chris