[exim] Regex for ACL condition - Cry for Help

I'd like to use an ACL to reject incoming spam, but I don't know
how to write it.

In my case I run mailing lists, and I get a fair number of emails
where the From and To addresses are a dead giveaway that it's
spam. My mailing list addresses have suffixes like -on, -off,
-vacation, etc. that are tacked on to the base list name.

For example, this email would be spam

    From: mylist-on@???
    To:   mylist-off@???

    
So I want to strip off the suffix, and then compare the base list
name of the Envelope From and Receipent To address. If there is
a case insensitive match, I want to reject the email.

Something like this

  drop   message = From and To address contain the same list name
         condition = ${if eqi {$0}{$1}  { match 
{$local_part}{^.*-(on|off)\$}} \
         { match {$sender_address_local_part}{^.*-(on|off)\$}} {1}{0}}

Actually, nothing like the above, but if you can whip out an Exim
ACL condition to solve this problem, I would appreciate it.

Thank you.

mark