controlling when a specific message expires

[Arnt Gulbrandsen <arnt@trolltech.com>]

I'm creating a fair bit of mail by putting files in POSTOFFICE/router. 
Works well. Reliable and efficient. I like it. But:

I send some autoreplies that are basically worthless when people
forget the mail they sent, things like "your mail to a@b has been
forwarded to c@d, please use that address in the future" and "your
message has arrived and we will reply within two business days". I'd
like to drop such auto-acks after an hour. Is there anything I can add
to my POSTOFFICE/router/123456 file to control expiry?

TIA,
--Arnt