list policies about vacation programs

[JC Dill]

I help manage a mailing list for ISPs, so it's a given that everyone who 
*belongs* on this list is highly technical, although it is becoming 
increasingly common that we get subscribers who are not highly technical 
(although they do work at ISPs).  A few days ago a vacation program started 
replying to every message posted, sending the reply back *to the list* (not 
to the message author).  I posted to the list that I had set the 
miscreant's subscription to nomail and would lart him when he returned from 
his vacation.

Since then I've received 2 forwarded emails regarding another subscriber's 
vacation autoresponder that is responding *to the author* for each post to 
the list. Since these messages are not going *to the list*, should I, as 
list owner, take any action (set their subscription to nomail, or ?) 
against the subscriber?

I see a couple of issues:

1)  The messages are not going to the list, but rather to the author.  In 
some situations, it IS appropriate to let a list poster know that you will 
not be reading and replying to their post in a timely manner.   But this is 
a pretty large list (~1000 subscribers), so maybe I shouldn't give any 
allowances for this, maybe I should insist that vacation programs not reply 
to posts to this list.

2)  I don't yet know if the vacation program is sending more than one such 
message to each poster, e.g. if someone posts several times a day, are they 
getting a response per post, or just a response for the first post.  Should 
my action be different if the vacation program sends multiple responses to 
the same poster?

Weighing these 2 issues, my present gut feeling is that I should not take 
any action if the vacation program is only sending *one* response to each 
poster, but that I should set the miscreant to nomail if the vacation 
program sends multiple responses when someone is posting multiple times.

Are there other factors I'm overlooking?

What I am seeking is not so much "the answer" as to make sure I've asked 
all the right questions to help me come up with the answer for my list.

Thanks!

jc