How to reply to many lists

[Robert Fields <robertf @ best . com>]

I run several large lists.  There are many people who subscribe to more 
than one of my lists.  At times I want to post a message to al the 
subscribers, like when I go on vacation.  If I just post to the lists, 
then some subscribers will see the vacation message once for each list 
they subscribe to.  Any suggestions on how to post a message to all the 
list members of several lists so each subscriber only gets one copy ?

Thanks in advance ...

-Robert