Reply emails automatically with Mail & AppleScript & Automator
You can do it like this:

property the_numbers : {10000, 20000, 30000}
using terms from application "Mail"
    on perform mail action with messages theMessages for rule theRule
        repeat with i from 1 to count of theMessages
            tell application "Mail"
                set the_sender to sender of item i of theMessages
                set the_subject to subject of item i of theMessages
                set the_counter to item 1 of the_numbers
                -- make the outgoing message (the reply)
                set the_reply to make new outgoing message with properties ¬
                    {subject:"Re: " &amp; the_subject, content:"Use this number-- " &amp; the_counter}
                tell the_reply
                    make new to recipient at end of to recipients with properties {address:the_sender}
                end tell
                send the_reply
            end tell
            -- this is the step that deletes item 1 from the list 
            set the_numbers to items 2 thru -1 of the_numbers
        end repeat
    end perform mail action with messages
end using terms from


This works, but you'll have to do a little work to get your list of numbers into an AppleScript list. You'll put them up at the top, separated by commas, replacing my 10000, 20000, 30000. 

I call the list of numbers "the_numbers". By calling it a property, we save the value of the_numbers from run to run. If you were to use my script as-is in place of your "Untitled 3" in the rule you've set up, the first time the script is called it will be working with {10000, 20000, 30000}. The next time it runs, the list will be {20000, 30000}. The next time it runs, it will be {30000}. It will also be {30000} for all subsequent runs. I am assuming/hoping that you have a very long list of numbers and you aren't going to run out.

A better script would let you know that the list of numbers was down to the last one.