Auto-reply to "reply-to" address?

[Papa Bear_Left]

G'Day

I want to set up an autoreply (aka vacation responder) that will send a reply to an email from something like, oh I don't know, a message sent via geocaching.com.

The trouble is that this email actually comes from noreply@geocaching.com (to continue the hypothetical example) and the sender's actual email address is in the "reply-to" field.

My mail server will only respond to the From: address, as will gmail's vacation and filter options.

Any thoughts from any of you clever and knowledgeable folk?

If it can't be done on the server, I do have an Ubuntu laptop running 24/7, but it's a ooooold one with scarcely enough memory to run Firefox so I don't want to also have Thunderbird running. A small footprint program or FF extension would be OK, though.
(The laptop sits where we go in and out of the house, displaying the time, the weather forecast and some headlines, etc.)