Hosting Email

How do folks handle email for their web startup?

I have my rails app handling all of its email chores beautifully using
sendmail and ActionMailer. New Account Confirmation, Forgotten Password
Email, Monthly Newsletter, etc. DNS points to our server using MX
records and we're good to go.

My issue is how do I handle my corporate email -- employee email, etc?
I would really like to use google's private label hosing capability (i'm
talking about google hosting johnsmith@mysite.com NOT
johnsmith@gmail.com) as the Mail User Agent (MUA). However, I can't
figure out how to get employee mail to bypass our web app and go to the
Mail User Agent while still maintaining the MX record link to our web
app for the web apps business(again, preferably google's corporate email
handling).

It's as if I need two sets of MX records -- one for the web app traffic
and one for our corporate/employee email.

What have other folks done? Am I missing something fundamental? For
example, is there a way to have sendmail accept all email but then
bounce the employee email over to an outside MUA (again, maybe google)?