MTA - MLM - DNS configuration question

[Eirik Dentz <eirikdentz@brainlink.com>]

I've been asked to set up a MLM along side a web server and I wanted to ask
a quick question to the experienced, before I put a lot of time into setting
this up.

My situation: I'm responsible for an web server that has sendmail installed
and is configured to send email via Perl and PHP scripts, but doesn't
receive any.  Recently my supervisor has asked me to set up mailing list
capabilities on the web server, because the IS department doesn't have the
capacity to do so at present and they want tight integration between the
mailing lists and the web server (web based subscribe/unsubscibe pages for
lists and archives).  Based upon various threads that I've followed on this
list and other research, I've decided to switch from sendmail to postfix and
to use the GNU Mailman MLM (I'm open to other suggestions...)

My question is this: The DNS is under the jurisdiction of the IS department
and the MX record @mydomain.org is set up to point at their email server.
Does it make sense and is it possible to set up another MX record:
@lists.mydomain.org which will point at the web server?

I realize that it is generally a bad idea to set up your web server to do
double duty as an email server.  Any ideas regarding at what message volume
a mail server will have a serious negative impact on a web server running on
the same machine would be appreciated.

Thanks in advance

eirik