I am not sure if we are quite talking about the same things.
The provider I use (see sig line and for info I do not work for them, just advertise their service since it is so good) provides a method for dealing with emails.
My understanding is that they have developed this addition themselves to the mail server.
Basically for each account I can upload a text file called .redirect and in that I can specify the handling of emails. (A web panel interface to the file is anticipated soon), I can redirect the email elsewhere (to one or more addresses), igore the mail, bouce the mail, autoreply with a fixed text file or send the email to a program (or any combination of these).
What I like to do for some systems is use a script to handle the emails, the script interprets the email and then handles it as required this can be any action including updating databases, uploading web pages, replying to the sender etc...
I am against systems which try to be interactive by using a cron job to check for new mail against a POP box because there tends to always be a delay in the processing of email, even if only a few minutes and on the sites which do this I tend to find it annoying (expecially an email based forum site I use).
If the flexibility of my supplier sounds like what you need then I would suggest giving them a try, if memory serves they offer a trial period so if you don't like them you can always get a refund.
I am sure that others may provide a similar flexibility but I have yet to find one.
If you do contact my host then please mention that I sent you , might get me some brownie points <grin>