[exim] temporarily suspend mail delivery to an account

Hi.

I wonder if it's possible to add to my Exim configuration file, a
section that would temporarily suspend mail delivery to certain user
accounts that are specified in a file. Once the account was removed
from the file, not only would delivery resume, but queued messages would
flow through as well. The sender would have no idea that the message
was not immediately delivered to the user in question. Any ideas? (This
would be used to do maintenance on a particular account -- moving it's
location on disk, etc. while ensuring no failures in the meantime.)

Jason.